I finally got a reply from bluehost this afternoon. Typical "We can't reproduce, give us the exact steps...blah blah" stuff ... I pointed them to their own forum's thread showing several people having trouble AND the vBulletin forum post about lots of vBulletin users having LOTS of trouble as a result.
With some strong words demanding they simply roll back whatever they did tuesday, I wasn't going to subject my users to the non-patched situation for an unknowable time while waiting for them to return to my issue. If they took 3 days to answer me, I wasn't going to leave the band-aid off for that long. I politely demanded they simply undo what they did.
This evening I decided to check ... and without the no-cache setting, my forum SEEMS to be acting right ... no further word from bluehost yet ... but things do appear to be happening on their end ... we shall see. For now, I'm running without the .htaccess mods.