I've managed to get it error free (for now) by working around the problem. I'm now using a TsPanel skinned as TOOLBAR, with TsSpeedButton's skinned as TOOLBUTTON. Also using TsPanel's skinned as GRIPH. But only for the top toolbar.
I've also been experiencing a lot of repaint issues, all of which are like this:
The black squares appear, which are probably the areas that still need to be repainted. This is acceptable, but, sometimes these areas remain black partially (in the IDE and in the built application).