That's very strange, Eric. I've grown AVs and other gessies--and other plants!--in three different basements in three different states, and haven't had problems. The only thing that occurs to me is the gas--I have read AVs at least act like 'the canary in the mine' for even very minor gas leaks, so it might be a good idea to have that checked. Can't think of anything else to suggest tho'. Good luck, and let us know what happens.

Maybe your basement is colder than the bedroom? You've probably checked the temperatures, but thought I'd mention it, just in case, because till I got a thermometer, I'd never realized how cold my basement was compared to the rest of the house. The basement was at 59-60 degrees when just about every other spot in the house was at 70. And I did lose a bunch of AVs to cold last winter. Though streptocarpus should not be as picky about temperatures, and you said your streps don't like it there either...

If its not the temperatures -- then could it be, somehow, that the lights in the basement are stronger?

Thanks for the suggestions.

The basement temps run fairly steady from 68-70, night and day. The upstairs bedroom is warmer, to the mid 70s or so with a nighttime drop to the mid to upper 60s. I had wondered if I was giving them too much light in the basement, but placing them in dimmer conditions didn't make a difference.
We're getting the furnace checked; while there's no detectable gas odor I'd like to rule out any kind of combustion problem, assuming that's even a possibility.