So I upgraded from 6.1 to 6.22 this morning. Installation was without problems. 6.22 even showed up with all effects in place {e.g. Roomverb, SFX Machine, etc} which actually kind of surprised me. I figured I would have to reinstall effects programs.
So here's the problem : when I opened a file I created with 6.1 and played it, the tracks that had effects added to them via an Effects window did not show up in the Mixer window. I checked the routing from the Effects window for those tracks (there were actually 3 tracks) and they were correctly routed from the Effects window to the correct channel in the Mixer window. The output for these tracks does show up with the proper level in the Tracks window.
All tracks that are not routed through seperate Effects windows do show up at the Mixer window and play properly.