Parts of plot dissapear during scrolling

[Uwe]

i created a horizontal "timing" diagram and i use a self definded symbol!

Guess you are using a QwtPlotIntervalCurve and you have overloaded QwtIntervalSymbol::draw() ?

If so show your code - if not throw all your code away beside that couple of lines you need to implement YourIntervalSymbol::draw().

Uwe