Custom commands change case.

I set up a custom command

cp %ff Copy_of_%ff

(That's a direct copy from the custom commands menu.) However, when I click that command, what I see is

500 'CP dragon Copy_of_dragon': command not understood.

(That too is a direct copy.) The command has been changed to upper case, so of course Unix doesn't recognize it. If I enter the command in upper case, it still goes through in upper case.