I've had no problems at all with inverted stuff or high negative G stuff.
The only problem I have now is that the 18x12 hybrid is ever so slightly too much on extended verticals. I will break the new engine in on the 18.1x10 and then play with the hybrid again, even if I have to cut it down a little.
Inverted is fine for me - problematic only with negative G. Airflow inside the cowl perhaps a bit fluky.
Got a couple more props to try. Xoar 18x10 standard gas/glow beech (85 grams![sm=thumbup.gif]) and an APC 15.5x12W pattern (105 grams). GravesRC did not have a 16x12 APC. Time before last when I flew, the 17x12 was a bit too much, so this 15.5x12W is the next step down. Also got an APC 18x10 sport prop to try just for the hell of it.
Really got my fingers crossed that the Xoar works out. I admire the work and thought you've put into the hybrid featherweights, but it'd be nice to have an off-the-rack prop that is fairly lightweight. However, already I suspect that the APC 18.1x10 airfoil is better.