change of apparent brightness--5DII in Manual

I've been recording 5DII clips in Manual. I take a still first, to check the histogram.
Then, whenever I start recording, 2-3 seconds into the clip the apparent brightness/exposure changes-- it gets lighter, often wrecking my carefully considered metering.
What gives?

everything is manual? even iso? are you using natural light, or florescences? any camera movement?

Firotechnics wrote in post #10896903
everything is manual? even iso? are you using natural light, or florescences? any camera movement?

I was going to say the same thing but add the user color settings superflat may help you out?

All manual,just shooting outdoors, no change in lighting conditions, tripod-mounted. Not sure what user color settings you're referring to. I've gone through the video settings options again to see if I might be missing something, but ?
Could it be a bug in the firmware update that allowed manual exp. control? Haven't seen any reports in that regard. I need to see if it happens in AV or TV mode.