Colloquy is to blame, then. The same thing will happen in 6.35 with Ctrl+R since that control code hasn't changed, meaning the problem has been around for quite some time (the reverse code has been around in mIRC since 5.x, so something like 10 years). It seems that Colloquy handles reverse as italic and the new italic as reverse, so perhaps you should file a bug with them for "incorrect" Ctrl+R behaviour-- and then while they're fixing Ctrl+R they can swap it with italic and everything will work fine.
