I believe I have found a bug in the manner in which Rescue operates with RTH. I have Rescue on Aux2 and RTH on Aux3. I have Stabi set to Acro and I have 1.2 seconds of delay before it goes upright.

If I am inverted and activate Rescue via Aux2, everything works fine. The model will level out inverted and the switch to upright in 1.2 seconds. I have some collective added and the model never goes downwards.

However, if I am inverted and activate RTH via Aux3, RTH starts to function but there is a large drop in altitude when the upright-delay times out and the heli switches from inverted to upright. The negative collective persists through and after the transition to upright.