diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0c5316f7..b8f1bf59 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
 
 ### Changed
 - `bashunit doc <filter>` says `No assertion matches '<filter>'` instead of printing nothing, which was indistinguishable from a broken install. Mirrors the existing `--custom` wording; the exit code stays 0 because `doc` is informational (#1201)
+- Docs: an empty entry in the `-e/--env/--boot` file assigns an empty value rather than restoring the built-in default, so blanking a boolean disables it; the guide said it "wipes" the value, which reads as a reset. The rest of the precedence ladder is now covered by tests (#1217)
 - Docs: the test-function name rule is stated correctly — the prefix is a literal, lowercase `test_`, so the guide's own `testRenderAllTestsPassedWhenNotFailedTests` example and its claim that names are case-insensitive were both wrong, and a function named either way is silently never run (#1215)
 - Docs: `assert_matches` runs `grep -E` in a subprocess per call — ~2.5ms against ~0.065ms for `assert_same`, about 38x — so hot loops matching a fixed substring should prefer `assert_contains`. The subprocess is required by the Bash 3.0 floor (#1187)
 - Docs: `assert_match_snapshot` warns that a `@data_provider` test shares one snapshot across all its values — the filename comes from the test function, so the first value creates it and the rest fail against its content. `assert_match_named_snapshot "$1"` gives each value its own (#1185)
diff --git a/docs/configuration.md b/docs/configuration.md
index 9fe60b51..82d7cdda 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -39,7 +39,10 @@ to lowest:
 The `--env` file is sourced during flag parsing, so it overrides `.env`, `.bashunitrc` and
 the ambient environment, and it loses only to flags written **after** it on the command
 line: `bashunit --simple --env custom.env` uses the file's value, `bashunit --env custom.env --simple`
-uses the flag. Unlike `.env`, an empty entry in that file does wipe a value.
+uses the flag. Unlike `.env`, an empty entry in that file is **not** treated as "not
+configured here": `BASHUNIT_SHOW_HEADER=` assigns the empty string, which is not the
+built-in default — for a boolean setting it simply is not `true`. Delete the entry to fall
+back to the default; blanking it disables the setting.
 
 An entry left **empty** in `.env` means "not configured here" and does not
 override the environment, so `BASHUNIT_OUTPUT_FORMAT=tap ./bashunit` keeps
@@ -53,7 +56,9 @@ always wins. `--skip-env-file` skips both `.env` and `.bashunitrc`.
 The two files are read differently, which is why they behave differently: `.env` is
 **sourced** as a shell script under `allexport`, so it can hold arbitrary shell and an
 empty entry is unconditional (hence the preservation rule above), while `.bashunitrc` is
-parsed as literal `KEY=value` lines and only fills names that are not already set.
+parsed as literal `KEY=value` lines and only fills names that are not already set. The
+`--env` file is sourced the same way as `.env` but without that preservation pass, which
+is why blanking an entry there assigns an empty value instead of being ignored.
 
 ## Benchmark reports
 
diff --git a/tests/acceptance/bashunit_env_precedence_test.sh b/tests/acceptance/bashunit_env_precedence_test.sh
new file mode 100644
index 00000000..67471b52
--- /dev/null
+++ b/tests/acceptance/bashunit_env_precedence_test.sh
@@ -0,0 +1,136 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# The configuration precedence ladder is six levels deep and every level is a
+# claim in docs/configuration.md that nothing executed. The two files are read
+# by different code -- `.env` is sourced with a preservation pass for values the
+# file blanks, the `--env`/`--boot` file is a plain `source` under allexport --
+# so the levels can drift apart without either side erroring.
+#
+# The blanking rule is the one that was documented wrong: an empty entry in the
+# `--env` file assigns the empty string, which for a boolean is not the default
+# but `false` (#1217).
+#
+# BASHUNIT_SHOW_HEADER (default true) is the probe for the file/environment
+# levels; BASHUNIT_SIMPLE_OUTPUT for the two that need a real CLI flag.
+
+function set_up_before_script() {
+  BASHUNIT_BIN="$(pwd)/bashunit"
+}
+
+function set_up() {
+  WORKDIR="$(bashunit::temp_dir)"
+  printf '%s\n' '#!/usr/bin/env bash' 'function test_ok() { assert_same 1 1; }' \
+    >"$WORKDIR/t_test.sh"
+}
+
+# Says "shown" or "hidden" for the run header. Every call is a fresh process, so
+# the ambient value is passed in rather than exported here.
+#
+# The "unset" case has to unset it *in the subshell* rather than just not
+# setting it: CI runs `cp .env.example .env`, and `.env` is sourced under
+# allexport, so the outer run exports BASHUNIT_SHOW_HEADER to every child. An
+# inherited value outranks `.bashunitrc` -- correctly, per the ladder -- which
+# made the `.bashunitrc` case fail on Linux and the two `--skip-env-file` and
+# `--env` cases pass for the wrong reason.
+function _header() { # $1 = ambient BASHUNIT_SHOW_HEADER ("" for unset), $@ = extra args
+  local ambient="$1"
+  shift
+  local output
+  if [ -n "$ambient" ]; then
+    output=$(cd "$WORKDIR" && BASHUNIT_SHOW_HEADER="$ambient" \
+      "$BASHUNIT_BIN" --no-parallel "$@" t_test.sh 2>&1 | strip_ansi) || true
+  else
+    output=$(cd "$WORKDIR" && unset BASHUNIT_SHOW_HEADER &&
+      "$BASHUNIT_BIN" --no-parallel "$@" t_test.sh 2>&1 | strip_ansi) || true
+  fi
+  # The header is colour-wrapped, so this must run on stripped output: an
+  # unstripped match silently never fires and every case reads as "hidden".
+  case "$output" in
+  *"bashunit - "*) echo "shown" ;;
+  *) echo "hidden" ;;
+  esac
+}
+
+function _simple() { # $@ = args; says "simple" or "verbose"
+  local output
+  output=$(cd "$WORKDIR" && unset BASHUNIT_SIMPLE_OUTPUT &&
+    "$BASHUNIT_BIN" --no-parallel "$@" t_test.sh 2>&1) || true
+  case "$output" in
+  *"Passed"*) echo "verbose" ;;
+  *) echo "simple" ;;
+  esac
+}
+
+function test_the_builtin_default_shows_the_header() {
+  assert_same "shown" "$(_header "")"
+}
+
+function test_bashunitrc_beats_the_builtin_default() {
+  printf '%s\n' 'BASHUNIT_SHOW_HEADER=false' >"$WORKDIR/.bashunitrc"
+
+  assert_same "hidden" "$(_header "")"
+}
+
+function test_the_environment_beats_bashunitrc() {
+  printf '%s\n' 'BASHUNIT_SHOW_HEADER=false' >"$WORKDIR/.bashunitrc"
+
+  assert_same "shown" "$(_header "true")"
+}
+
+function test_an_env_entry_with_a_value_beats_the_environment() {
+  printf '%s\n' 'BASHUNIT_SHOW_HEADER=false' >"$WORKDIR/.env"
+
+  assert_same "hidden" "$(_header "true")"
+}
+
+# "Not configured here": .env snapshots and restores values it blanks.
+function test_an_empty_env_entry_preserves_the_environment() {
+  printf '%s\n' 'BASHUNIT_SHOW_HEADER=' >"$WORKDIR/.env"
+
+  assert_same "shown" "$(_header "true")"
+}
+
+function test_the_env_flag_file_beats_dot_env() {
+  printf '%s\n' 'BASHUNIT_SHOW_HEADER=true' >"$WORKDIR/.env"
+  printf '%s\n' 'BASHUNIT_SHOW_HEADER=false' >"$WORKDIR/custom.env"
+
+  assert_same "hidden" "$(_header "" --env custom.env)"
+}
+
+function test_the_env_flag_file_beats_the_environment() {
+  printf '%s\n' 'BASHUNIT_SHOW_HEADER=false' >"$WORKDIR/custom.env"
+
+  assert_same "hidden" "$(_header "true" --env custom.env)"
+}
+
+# The documented difference from .env, stated in terms of what is observable:
+# the entry overrides, and an empty value is not the default. With the default
+# being `true`, a wipe-to-default would show the header; an empty string does
+# not equal "true", so it hides it.
+function test_an_empty_entry_in_the_env_flag_file_is_not_the_default() {
+  printf '%s\n' 'BASHUNIT_SHOW_HEADER=' >"$WORKDIR/custom.env"
+
+  assert_same "hidden" "$(_header "true" --env custom.env)"
+}
+
+function test_skip_env_file_skips_both_files() {
+  printf '%s\n' 'BASHUNIT_SHOW_HEADER=false' >"$WORKDIR/.env"
+  printf '%s\n' 'BASHUNIT_SHOW_HEADER=false' >"$WORKDIR/.bashunitrc"
+
+  assert_same "shown" "$(_header "" --skip-env-file)"
+}
+
+# The --env file is sourced during flag parsing, so it beats a flag written
+# before it and loses to one written after.
+function test_a_flag_before_the_env_flag_file_loses_to_it() {
+  printf '%s\n' 'BASHUNIT_SIMPLE_OUTPUT=false' >"$WORKDIR/custom.env"
+
+  assert_same "verbose" "$(_simple --simple --env custom.env)"
+}
+
+function test_a_flag_after_the_env_flag_file_wins() {
+  printf '%s\n' 'BASHUNIT_SIMPLE_OUTPUT=false' >"$WORKDIR/custom.env"
+
+  assert_same "simple" "$(_simple --env custom.env --simple)"
+}