"Exclude types" - apparently some filetypes can't be excluded?

[lloyd]

In the "Exclude types" field of the Source Options tab associated with an entry in the custom catalog items, most filetypes I add get converted to the long-form name of the filetype. For example, .otf becomes "TrueType OpenType font". Some filetypes don't seem to be recognised as they remain as abbreviations: .pfm and .afm, for example, stay as they are after being entered. Of course it wouldn't matter how they appear in the list, but these ones that aren't recognised don't actually get excluded as requested, and they end up clogging up my catalog.

Am I doing something wrong?