If % is a valid prefix, Bahamut should list % in the raw 005 response under CHANTYPES. mIRC should handle it properly, in that case. I don't think this is mIRC's fault.
Keep in mind that if Bahamut returns the channel as %CHAN, it better mean it. Even if mIRC didn't filter this channel, it could only assume the channel was actually called %CHAN, and double clicking it would /join %CHAN, not #CHAN. I assume this is valid?
