Not only UC or LC makes problems. Also the sorting order of special charcters, e.g. "-", "_", is tricky, except "!" which runs on top every time ... leading to that damned "!" ... "!!" ... "!!!!!!" prefixed names.

But in all some poser programmers have great difficulties with all directory path's and it's equal if in relative notation with ":" or in absolute windows notation.
Poser tend's to take the first file with a matching filename. This was all time given for all texture files but in P7 I found that this will also happen to obj-files from geometries folder. If loaded via library tab it's ok. After saving as pz3 and loading again sometimes the wrong file is used.
And it doesn't make any difference if that file(name) is located in one or several runtimes.
The only way around is in renaming that files ... and change that all to cr2, pp2, pz2, etc.

Quite annoying ...