I think you might have been tripped up by your knowledge of Perl here.

Thanks, but I think you're being far too generous here :) I was being incredibly stupid and even the warnings pragma didn't help because I was using exists. I spent quite some time debugging keys -- and it took a long time between runs to generate those keys -- before I realized that my keys were perfectly valid the first time I created 'em. It's things like this which make me drool for Haskell at times (where I can validly use the variable prior to the declaration and assignment (well, it's not really declaration and assignment, I suppose.))