Install SMF 2.1
http://www.simplemachines.org/community/index.php?topic=485590.msg3399931#msg3399931 or the latest repo.
Make a copy of the default theme.
Change your profile to use the new theme.
Try making a post - editor is broken with the new theme.
It's not just the editor that's broken. The whole admins frontpage is broken as well. So is the Error Log page. And there are probably more.
You mean on the copied theme?
Yep
Weirdness. Could be a paths error. Ema will fix it. :D
Aha. I noticed that the copied theme only has index.css and rtl.css and theme.js. I bet all the borkiness is due to the copying thingy not being updated to take account of extra files in 2.1. Some of those will end up being called from default anyway (once things are a bit more sorted). Some of them will need to be automatically added to any copied themes.
Can't seem to reproduce this on 2.1 current.