As stated, you should not be using quotes in identifiers unless otherwise noted in the help file. Quotes are only necessary in commands where mIRC tokenizes $1- by $chr(32) (space)-- in identifiers, $1- is tokenized by $chr(44) (comma), so $2 is already: Dejavu Sans Mono. This is not really a bug. There are instances where mIRC accepts quotes as a convenience, but I don't think mIRC should make a habit of doing that.
