It's not a bug, it's just for a better listing design...
From what I can remember the file must be 25 file length and I ignore everything that is not .mod
I can of course add .MOD or .Mod and .mOd
but the original amiga format is "mod.name", so if you have to rename it, just rename it "Name.mod"
So you'll have a better display.
For ClassicWB try to deactivate KingKon...might be in the user-startup