this topic is old, but whatever: A few people reported that they had problems to sit on a sim. It looks very similar as the problem here. I didn't had any problems and only this person had the problem. The next day, it was someone else. Today, it's me ! The others doesn't have the issue anymore. It's really weird. I tried almost everything with my 11 years experience on SL (doesn't mean at all that I know everything but I've handle a lot issues in the past - but nothing like this one).
I bet that tomorrow it will works again for me and the problem will occur with someone else.
Well yeah. It was just to let you know as it's the closer issue I found with Google.