Yes, my very first thought was a loose arbor bolt. However, I ran through several scenarios and each one failed to cover it. The biggest reason is because this is a TS55EQ, and it doesn't have the friction slip clutch. So the blade will freewheel if the arbor bolt is even slightly loose. The second is because the alignment keys won't allow a loose arbor bolt to self-tighten, like what a tablesaw arbor will do. I even considered the extreme situation of the bolt being so loose that the alignment keys were not engaged, but it takes 1-1/2 turns of the arbor bolt to close the difference between the keys being misaligned and aligned. So when the keys did align, the arbor bolt would still be a full turn loose, and the blade would still freewheel.
So the only way for the alignment keys to get damaged and the arbor shaft to cam out, is if the arbor bolt was fully tightened.
P.S. I'm still trying to come up with a clever comeback for the "Ick", but your name has so many F's, OO's and L's, nothing is coming to mind. I'm sure I'll think of a good comeback soon though. [big grin]