1: Thanks guys. It's really strange - today I opened up a new BIAB session, and, after confirming that the midi problem I detailed in my initial post was still afflicting my project, I went into 'MIDI/Audio driver setup' and looked over what everything was set to, and then simply clicked "OK" without making any changes whatsoever, and voila!, I immediately began hearing my midi synth (Forte) again, when playing from my external controller, and there's no latency when I click the on-screen keyboard now. Amazing, I did absolutely nothing but click 'OK' on my existing settings. Maybe BIAB just likes to be reaffirmed sometimes(?)

2: On the strings patch not muting, I tried resetting all bars and then re-doing the bar mute, but the problem persisted. I would also click on 'Play' instead of 'Replay', to try to give BIAB the idea that I wanted it to give the thing a fresh start. Still no joy. So I chose another style and... suddenly it started muting fine at the correct bar. So I switched back to the "problem" style, and said a little prayer. Voila! again! It now mutes correctly. So happy. I don't understand it but I'm happy. (btw, this bar muting problem never did occur when starting a new song - it seems to have been confined to just that one project, so I guess something about it was just messed up...)

3: As for the out-of-sync recorded audio track, I've always had 'ASIO Always On' checked, and I'm wary about changing the audio driver since I had a heck of a time trying to get rid of error messages when I messed with it a couple years ago or so. Granted, it was an older version of BIAB - maybe it's not so touchy now. But back to the ASIO thing - I've got the buffer set pretty high (the ASIO window just shows "maximum" and "minimum" - no actual milliseconds - and mine is set to just under max, probably because I was having problems with Omnisphere last year...). Maybe I should back off the big buffer now. But what I don't get is why my recorded audio plays almost a full beat too SOON. When I think of latency, I think of things "lagging behind" and playing too LATE. Could it be that my audio is playing correctly but the rest of the "band" is playing late? Whichever it turns out to be, I should mention, I didn't have this problem before updating to 2010.5, if that gives anyone a clue about what might be happening.

Anyway, so that's my one remaining issue at this point. Thanks again for the feedback, and for anything further.