Again, that's not because of the footage -- it's because of the processing within Vegas. The 150's footage is 8-bit.
To date I have only seen this Vegas pixel "banding" when working with HMC150 video, other consumer cameras I've used ( Canon HG21, Canon HF S10, Sony HDR-XR520V ) produce AVCHD video files that do not display this problem. Switching to 32-bit "Pixel Format" cures the problem.