Toggle Button display problems

I have a long vertical line of PtToggleButtons, spaced fairly close
together. They each have height 20, and there is a 20 Y difference between
each pair.

The problem I have having is that, fairly often, a few of the toggle
button’s buttons turn black - i.e. you can no longer see the state of the
toggle button. Another window dragged over the toggle buttons can cause
this, among other things. Also, spacing the toggle buttons closer together
than their height makes the problem worse, but spacing them farther apart
than their height doesn’t totally fix the problem.

This seems to be a redraw problem - is there any way around it?

Stuart Harding