Builtin file browser search is broken

[sim642]

In ~/Downloads, when searching for "these", sioyek shows: However, when searching for "Halbw" in the same directory, it shows: Both of the latter file names contain "these" but weren't found by the first search!

And before anyone asks, that filename has normal ASCII text, not some strange unicode characters:

$ python
Python 3.12.3 (main, Aug 14 2025, 17:47:21) [GCC 13.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> "Halbwachs.Nicolas_1979_these".encode('ascii')
b'Halbwachs.Nicolas_1979_these'