Overlapped DropAreas don't work as expected

Currently, it isn't possible to drop plottable items onto the plotting chart if the plotting plugin is floating on top of ign-gazebo's 3D view. It's possible to drop onto the plot if the mouse's path doesn't pass over the 3D scene though:

This happens because the moment the mouse enters the 3D scene's DropArea, that's holds focus, even when the mouse is on top of another DropArea above it. I haven't found a good way of working around it. Apparently one way of fixing this is to make one mouse area the child of the other one, but since they're in different plugins, that could become messy.

Another thing I tried was to increase the Z height of the plot's drop area, with no success.