https://bitcointalksearch.org/topic/m.3443712
Well - hopefully it's the same problem! That's how I stumbled upon this thread in the first place, remember? We seem to confirm each other's findings re the test-builds, i.e. we both consistently get zombies and/or decaying hash-rates on the builds we've tested, but perhaps I see them more quickly as I'm running 34 erupters. Anyway, at the moment I'm happy with 3.5.1. It's been running about 4 hours in total and no errors, so hopefully it will survive overnight and become my new "stable" build.
As an aside, I have 2 * 7970's in my machine also, but they are happily mining LTC using another instance of 3.3.1 (I'll upgrade that to 3.5.1 at some point, even though it's not strictly necessary).
I haven't bothered trialling the latest test-builds. I'll just leave 3.5.1 running until morning and see what ckolivas makes of all this.