[Peter Mccall]

I can confirm the OP’s problem.
Both 32 and 64 bit versions of Vegas 9.0c are affected.
Earlier versions are fine.
There are no settings that I can make that will render without this flickering. Actually, it’s not really ‘render’, it’s the way Vegas plays AVCHD. You can see the problem just by playing the timeline. If you step through a frame at a time, you can see the picture dim every so often, with broad diagonal stripes. At normal play speed it looks an awful lot like a copy of a Macrovision protected VHS tape (so I’m told!).

Something happened in the 9.0c release to cause this because, as I say, version 9.0 – which I’m having to use – works perfectly.