Well, that was easy.. called TMO and they were able to reproduce the behavior, so they called RIM, gave me a case #, and talked to someone who checked the Requirements documentation. He wasn't sure why my device was doing what I described so..
.. he walked me through a firmware re-installation (manual backup, erased all applications [via Desktop Manager], then loaded .107 again). Worked like a charm!
This also fixed the problem I was having where ringers [for data events only!] would not come through the earpiece and they'd also stop the music. Now the music still plays and the ringer plays simultaneously. Woo hoo!
Alas, not a perfect score though.. the ringer still plays through the handset speaker when a call comes in. I'd at least
like it to play both places (earpiece & speaker). So many times I'll be walking down the loud street and won't hear my ringer cuz it's not coming through the earpiece.