refreshing touchscreen

I'm developing a Qt graphical application with different tabs for a 7" touchscreen connected to a SBC made by Variscite based on OMAP 35xx (from Texas Instruments). My O.S. is Linux-based (Ubuntu 9.10 - Qt is the latest 4.6.2).
Well, I arranged two tabs with different pushbuttons and other items on them; when I checked it on my PC, all was OK. When I uploaded my application on the SBC, 7" display shows problem when I changed from a tab to each other (small zones or "pieces" of previous shown tabs still remain on my current tab). I could define a video refresh problem.
Touchscreen is refreshed when I touch the top bar of the window (where title bar is contained): only doing so, I can see my tabs with no defect.
I noticed problem is directly connected to the AUTOFILLBACKGROUND property: if I don't use it (i.e. setting it to "false") no problem appears. But when I set it and use a Window color inside palette, I found this unpleasant effect.
Any idea?
Thanks
Paolo