Hm, but I haven't made any change in this area between the version you tested and build 1842.
Does it not work even under load ?
Could you please attach a debug file from this build ?
No, You weren't see thing or the reverse of that. GPU Util was indeed coming and going when I first installed it too, both on the new Gadget and in the sensor list. It was happening to fairly frequently so I didn't try to capture anything and besides Martin I don't have the time right now. If I see it happening again for long enough periods of time and I have the time I will try to document it.