Resolve 15.1.2.008 Studio and Wave Panel

I occasionally do pregrades at home on a mid 2010 Mac Pro with a wave panel to make my life a little easier when I do the job for real elsewhere. The first time I tried to do this using 15.1.2 Studio I hit a snag regarding power windows. Say I had a couple of soft edged windows based on circular power windows either side of a presenter doing a piece to camera - to lower the background, so far so good. I then come back to this shot after progressing a few shots down the line and decide to trim the position of a window. As soon as I grab pan (or whatever) the window size and shape then reverts to a central circular window again. I can undo this and continue as planned, but this is consistent behaviour and rapidly becoming a bit of a pain. Everything was fine on Resolve 14 (non studio). I'm running High Sierra and a GTX680 if that makes any difference. Anybody else seeing the same strange behaviour?

I should have added that the wave panel is running the latest firmware. If I trim the power window position using the mouse and GUI, the result is good. Only via the wave panel do I see a problem with the sizing reverting to a central circular window.