This the only time I have seen this happen. Some how the weigh and size of this piece of oak was near my limit and it may have been causing the problem.
I recently put a new conveyor belt on the machine. Got it from Jet. I had been fighting with a belt from WoodCraft and was very pleased the Jet belt went right on and tracked properly. I suspect it's a tad too loose and it slipped on this big heavy piece. It has not given me trouble on smaller lighter pieces. Now that I think of it, it has been sitting for a month or more so I wonder if the belt relaxed a bit? I take extremely light passes and try to run the conveyor at full speed.
This is an older machine and does not have some of the fancy new features like the Inteli-sand or the feature that tips the bed into and out of parallel with the drum.