Thanks for your bug report. I tested the feature and it is working correctly. As described in the help file, this option will filter out channels that begin with characters that are not numbers or letters.
Some time ago, it was extended to treat ##channels as seen on Freenode as normal channels, as this has become a standard prefix format. It could be extended again to treat [chanprefix][chanprefix]text as valid prefixes, ie. two channel prefixes in succession, assuming that these are now standard prefix formats on some networks.
