Compilation buffer fontifies some parts

Question

Here is a normal compilation message:

Here is what I have:

When I describe-char [...] I have the following description:

             position: 191 of 752 (25%), column: 0
            character: F (displayed as F) (codepoint 70, #o106, #x46)
              charset: ascii (ASCII (ISO646 IRV))
code point in charset: 0x46
               script: latin
               syntax: w    which means: word
             category: .:Base, L:Strong L2R, a:ASCII, l:Latin, r:Roman
             to input: type "C-x 8 RET 46" or "C-x 8 RET LATIN CAPITAL LETTER F"
          buffer code: #x46
            file code: #x46 (encoded by coding system utf-8)
              display: by this font (glyph code):
    ftcrhb:-CTDB-Fira Code-bold-normal-normal-*-18-*-*-*-m-0-iso10646-1 (#x22)

Character code properties: customize what to show
  name: LATIN CAPITAL LETTER F
  general-category: Lu (Letter, Uppercase)
  decomposition: (70) ('F')

Here is a ‘nil’ button labeled ‘File "src/tests/test_monomorphize.ml", line 5, characters 10-28:’.


There are text properties here:
  action               #<subr F616e6f6e796d6f75732d6c616d626461_anonymous_lambda_45>
  button               t
  button-data          nil
  category             t
  compilation-message  [Show]
  display              "[…]"
  follow-link          t
  font-lock-face       (button underline)
  fontified            t
  help-echo            "mouse-2: visit this file, line and column"
  keymap               compilation-button-map
  mouse-face           highlight

I started emacs with no init file and I have the exact same behaviour as you can see here:

My emacs version is 29.0.50

I thought it was a font-lock problem but even when disabling it it didn't change anything.