strange display bug

["Lawrence A. DeLuca, Jr." <HENRIK@MIT-MC.ARPA>]

I had two windows, the upper window at the top of a file, and the lower
window at the middle of the file.  I was in the lower window, typed

c-X o c-X b Return c-U c-X ^ c-X o c-X o Help l and here is what happened:

I moved to the upper window and selected buffer Main.  As soon as I
expanded the upper window it redisplayed the lower window!  It showed
the top of the file instead of the middle, ie, that which used to be
in the upper window.  As soon as I moved back to the bottom window it
correctly redisplayed the middle of the file.  What is going on here?