It's a design flaw in the original IRC protocol: a /names-reply only contains either a @ or a + prefix for a nickname (or neither, of course), but never both. From section 6.2 of RFC 1459:

Code:
        353     RPL_NAMREPLY
                        "<channel> :[[@|+]<nick> [[@|+]<nick> [...]]]"

I.e. the problem is inherent to the protocol, and neither IRC servers nor mIRC can do very much to solve it, at this point. Given the limited extra abilities that voice gives to people, the issue is considered to be not that important.

Saturn, QuakeNet staff