I've taken this out of page 6 the GF2 Stable settings Thread http://personal-view.com/talks/discussion/2321/gf2-stable-settings/p6

GF2 is a strange camera in Video mode. Panasonic say in their manual that Flicker Red (Flicker reduction) when set to 1/50 >1/120 in video mode will lock the shutter. I agree from the tests i have done in bright daylight that it does, however it appears SOMETHING is changing when large amounts of light or dark is introduced quickly, it seems to have a trigger point. If you use a manual lens, set aperture, use an ND or VariND and set iso to 100, it appears you can shoot and lock shutter between 1/50 and 1/120.

In dark situations where the camera needs gain, i think the iso will follow a similar pattern, jumping at trigger points, but shutter and iso will be locked at what you set it to unless you pan the camera to a very bright or very dark area, this seems to trigger some change but not enough to correct exposure. Weird. I throw this out there for discussion, as there seems to be conflicting opinions on this and no real explanations on what the camera is doing.