How to match upper case letters in filter?

General Discussion
1

I am trying to match consecutive upper case letters but neither of the following work

composer MATCHES (?-i)\u\u
composer MATCHES (?-i)\L\L

Matching consecutive lower case letters works ok with \l\l or \U\U

I think it must be a bug.

2

I think both variables have to be in lower case, e.g.
%_FILENAME% MATCHES "(?-i)\l\U" does not work
but
%_FILENAME% MATCHES "(?-i)\l\u"
filters all filenames where a lower case letter is followed by an upper case letter e.g. AudioTrack

3

It's bugged.

Workaround:
"$if($eql($regexp(%title%,\u\u,),%title%),yes,no)" IS no