This is surely not critical, but the UI appears to be a bit sluggish, e.g. window redraw is not immediate and quite slow. You could recheck the main input loop of your program and maybe look at MUI examples on how to do this in a proper way

Also, on heavy fragmented partitions checking the partition can take several minutes with 100% CPU load and the only way to abort this seems to be a reboot. How about a progress window with an abort button?

Another thing I noticed is that the "status" list in the main window has its input set (MUIA_Listview_Input, TRUE), so I can select entries in it for no apparent reason which is a bit confusing. Maybe this behaviour can be changed too.

Haven't checked much else but if I do, expect more to come