TypeScript union members in a function return value highlighted inconsistently

[Nicolapps]

JavaScript and TypeScript Nightly version: 5.9.20250330

When returning a union from a function in TypeScript, the first member of the union is rendered inconsistently.

export function myFunction():
  | null
  | null
  | null {
  return null;
}

The first | is rendered as mtk5 while the other ones are rendered as mtk1. This is an issue for color themes where both are rendered differently (e.g. the default Monokai theme). Similarily, the first null value is rendered as mtk17 while the other ones are rendered as mtk16.

This might be the same bug as #997. #1043 and #1041 also seem related.