Firstly, because combining +m and +i is not a good thing 99% of the time, the reason to go +m is to shush trouble makers in the channel while you ban them..etc +i is only if there is a larger issue.
Secondly, because adding $+ is completely and utterly not needed in #$chan line. I have tested it on NNS and 6.35, and others have on 6.34 and not had any issues.