This bug is probably the same issue, but the reporter
didn't give any info and thus it was closed.:
https://sourceforge.net/tracker/?group_id=31577&atid=402788&func=detail&aid=726225

Here's an example of how it's broken:

http://twistedmatrix.com/users/roundup.twistd/twisted/issue?%3Acolumns=id%2Cactivity%2Ctitle%2Ccreator%2Cassignedto%2Cstatus&%3Afilter=status&status=-1%2C1%2C2%2C3%2C4%2C5%2C6%2C7&%3Apagesize=50&%3Astartwith=0&%3Asort=activity&%3Asortdir=on&%3Agroup=topic

Notice that it's displaying multiple "documentation"
groups -- there seems to be no good reason for it doing
that, at least that I can see.

Similar things happen when you group on nosy.