Restore client-side layout after attach()/detach()

Hello,

I have written my own AddOn, where I use a lot of graphical gwt-stuff on th client side to draw lines, rectangles etc. Everything works quite fine except when I use tabs/tabsheet. When I open one tab which uses my AddOn (via button click I can draw lines etc.) and afterwards I open another one and switch back to the first, everything is gone. No lines etc. are anymore visible.
I guess it has something to do with the attachment/detachment of the ui-components when I switch the tabs. Is it correct? What is the right way to solve my problem? Do I have to repaint everything manually when the component is re-attached? How do I get the information about re-attachment? ? Are there some mechanismen in gwt to do this automatically?

Thanks!