I can use and edit tails just fine, but if I click on the tail button, which I'm told should let me edit ears or wings, my client instantly crashes entirely.

Other people using my exact same install seem not to have this issue.

Can you provide me with a crash report?

Same here! :P
http://puu.sh/cw9U7/74d8b1bf50.gif
^- Crash report included, also had an idea where it is being caused.

~ Greets.

I'll have to get my crash report when I get home from work. Sorry I forgot to include it the first time.