Did you ever resolve this? I just noticed something similar with mine. The top portion of the monitor is darker than the bottom. I think the backlight may have gone on it. That's some shitty quality control from philips. Monitor's 2 years old :/
Edit: turns out monitors have a 48 month...
Yeah it's pretty annoying. Especially when it happens multiple times in a row. It seems like a handshaking issue to me but who knows.... and I agree, as long as it's not a problem with the monitor itself I'm ok with it as annoying as it is.
Mine does the same thing. It's pretty random though.
Edit: I updated my drivers recently and the problems' gone away!
Edit2: I take it back, it still happens :p