I use a scalepane to display HTML within application.
Issues:
1. The scrollbar is resized, too. This might make it unable to get, if the sizing is to smal
2. When taking the scrollbar and moving (here to the right) it scroll slower then the mouse is moved. (scroll depending on scaling)
if the scrollbar is inside the SCALEPANE then what you describe is exactly what happens...
Only chance: put the SCALEPANE inside the SCROLLPANE... - well in your case I believe you embed some whole HTML page via IFRAME, so this is not really an option.