bizzare text scrolling

[Tim Johnson]

I've been using GNU Emacs 21.4.1 on kunbuntu 7.04 amd64 for a couple of
months now. I originally installed emacs from the debian repository via
apt-get, and it has worked just fine.

I just re-installed emacs from aptitude, which is the gui-based 
version of apt-get. I am now seeing some very strange behavior.
Specifically, text in a buffer will start *scrolling* - I've seen this
happen in *scratch* where as best as I can tell, words like "zoning" appear.

This also occurs in source code files - which is really alarming.
Although when I apply some action to the buffer, like a mouse click
or keystroke, the scrolling stops and the buffer (appears) to revert
to the original content.

Any ideas on how to make this stop?
thanks
tim