I went in your trap. The TextLayout layoutTooltipText() is a static method, so I see no way changing that without rewriting the polymorphic getTooltipBounds() and drawTooltip ():
About the not showing up, any chance, you disabled the setInterceptMouseClicks() on your component or one of it’s parents? It blocks hitTest and therefore mouseEnter and mouseExit as well…
Just a shot in the dark…
Ok I got it. The problem was that my custom components had child components themselves, which were screen filling. And the tooltip only shows for the uppermost component.