While shaking the proverbial trees among my industry peers for info on the Raider incident, I was told in passing about the tail rotor prop chucking a blade in the test pit on an iron bird rig a while ago.
Supposedly this was caused by some miscommunication regarding design loads with a supplier, and subsequently slowed progress as all changes were much more thoroughly scrutinized.
Same sources also relayed something that a lot of people have been suspecting - that the vibration is a large issue and the pilots were having difficulty reading displays in flight. Sounds like there is an internal belief that the fuselage may not be stiff enough.