Helmet Fire,
I have experienced the BK pitch up a couple of times and in different machines, One with a SAS system and the other with AP.
It tended to happen at 60% matched TQ in the cruise. Each time it happened there was some kind of turbulence about be it from CU or TS/CB activity in the area.
It only managed to hit the stops on one occasion, a bit un-nerving, but it came good with full forward cyclic and no collective movement. Recovery was not too dramatic, it came back fairly gently after about 35-40 degree pitch up and only lasted about 5 seconds all up. I think the trick is to feel it and catch it early as I have had it happen to various degrees on other occasions and with quick reaction on forward cyclic it knocks it on the head and it doesn't get out of control.
Someone mentioned the tendency for the BK to tuck into a RT turn at high bank angles below 40KT. I don't have a RFM with me for the BK at the moment but I am pretty sure the BK117-B2 manual has a warning note about this somewhere... You might be able to find it in your RFM??
Welcome to the BK pitch up club!!!