If the data on the screen looks wrong, the first thing to do is see whether the text is actually wrong. Type C-l, to redisplay the entire screen. If the text appears correct after this, the problem was entirely in the previous screen update.
Display updating problems often result from an incorrect termcap entry for the terminal you are using. The file etc/TERMS in the Emacs distribution gives the fixes for known problems of this sort. INSTALL contains general advice for these problems in one of its sections. Very likely there is simply insufficient padding for certain display operations. To investigate the possibility that you have this sort of problem, try Emacs on another terminal made by a different manufacturer. If problems happen frequently on one kind of terminal but not another kind, the real problem is likely to be a bad termcap entry, though it could also be due to a bug in Emacs that appears for terminals that have or lack specific features.