I just wrapped a talking head shoot against a white backdrop. The subject talked with his hands a lot and I noticed a ways into the interview that his hands would "disappear" when they were in motion (frame-by-frame above; click for closer view).
I shot this on a Varicam with a Fujinon zoom lens in 23.98, 180 degrees / 1/48 shutter. I also had my GH2 running for an alternate angle (1/40 shutter), and it also exhibits this issue though to a lesser extent.
I speculate that it has to do with shutter angle. Perhaps the constant light being reflected off of the backdrop was overwhelming the blurred frames. That would be my guess anyway, but I am posting it here to see if anyone else has come across this before.
This video, for the band Aloosh, is currently unlisted, but I thought I'd come and give you guys a sneak preview as this is my favorite online hangout ;)
All shot in Snowdonia using FS700, there's a lot of tasty treats getting made and broken in sloooooooow motion here....
You can watch part one here if you've not seen it already:
The band's album can be heard at www.aloosh.co.uk if you're interested...