Icon corruption in InDesign CC using PlatformIconClass

I'm porting an InDesign plugin from mac to windows. It supports InDesign CS5.5 through to CC2014.

I'm displaying a PNG image using PlatformIconClass with the code:

PlatformIconClass theIcon;

theIcon.LoadIcon(myPluginID, myRsrcID);

PMRect frame = GetFrame();

frame.MoveTo(0, 0);

ContentToWindowTransform(&frame);

theIcon.Draw(viewPort, ToSys(frame), kFalse);

The RsrcId is for a PNG specified in the fr file with PNGA etc as standard.

In CS5.5 and CS6, it displays fine. However CC shows image corruption (see screengrab - left is 5.5, right CC). Any ideas on what's causing this and how to fix?

Thanks

Liz