PMV for OS/2 v3.51 build 24318
Open FOC, choose a dir that contains filenames with capitalized extensions, eg
IMG_0013_b.JPG
IMG_0014_b.JPG
Use external utility to change case of filename extensions:
IMG_0013_b.jpg
IMG_0014_b.jpg
In FOC, use <F5> (or RMB->Refresh). PMV will not update filenames for thumbnails.
Very much worse, if you then load a file, the main window inherits the filename with the wrong case extension, with the possibility of saving it wrong as well. This makes this issue a bug and non-cosmetic.