I have a field of type Selection named "Point Of Use":

If I create an Advanced Filter to search the "Point Of Use" field with these settings (observe the "HQ" in UPPERCASE):

the result is:

However, if I changed the search text to lowercase as in:

the result becomes a mish-mash of:

This does not happen (the mish-mash) if field "Point Of Use" were a Text field.
IMHO, this 'inconsistency' could be addressed by at least two ways.
(1) For a Selection field, the logic could be to use the function strtolower() at the moment of comparions. I.e.,
Compare strtolower(search text string) with strtolower(value of the "Point Of Use" field's content)
or
(2) Provide a "Search is case sensitive" checkbox if the user wants to enforce a case-sensitive search on searchable fields. As in the mock-up image below:

reference: https://moodle.org/mod/forum/discuss.php?d=316460

Cheers
Frankie Kam