Arg, I was right about the upcoming meeting having the same problem...
The previous one has stopped reminding me now (and is no longer filling my deleted items folder with unsent tentative responses), but now another meeting is doing it.

In the time it took to write that previous sentence, I've had 3 reminders. Driving. Me. Mad.

And there's two more upcoming meetings creating unsent meeting responses in my deleted items folder as well... What the hell is going on?? D:

Any suggestions would be much appreciated. Just tried disabling cached exchange mode, and it didn't help.