Windows GUI palimpsest

Windows (both XP and 98) seems to have a problem with our GUI, written
using R's tcl/tk package.

When we open another window, and then return to the GUI, the GUI has old
pieces of text left from the previous windows and/or places which are
cut off where a window had been.  

Also, when it computes something, the window will often decide to move 
itself over for no apparent reason, so it moves one button at a time,
very slowly --- this doesn't happen under linux or Mac.

Is there any way to stop this from happening?