it's all in the title: if a group is muted, i can't solo any of its tracks.
this doesn't seem consistent with Live's soloing behaviour where you can solo a track even if it's muted, or if it's routed to a muted track.
Not quite: in Live 7, if a track is routed to another track, and this receiving track is muted, soloing the first track doesn't "work". It's the same with groups.
If a track is itself muted, it can still be soloed, but not if it's routed to any muted track.