Broken behavior related to this happens quite often actually. I've had sites that were bitten by this or some variant. If you follow the Facebook bug tracker it

Broken behavior related to this happens quite often actually. I've had sites that were bitten by this or some variant. If you follow the Facebook bug tracker it comes up every now and then (it might be localized to a degree in some cases). They do move fast and I think fix it quickly in most cases. In fact there was something that was broken just last week here on HN but the behavior wasn't something that affected so many sites to this degree.