If the data stream written by less does not fill an entire screen, leftover
data, the contents of the screen as shown just prior to exit from the
previous execution of less, fill the remainder of the screen.

This  is extremely annoying.  (<rant> It is particularly bad when looking
at man -k output, small man pages, small files, etc, etc.   I like a large
terminal window and that only makes it worse.  </rant>)  Often it is
virtually impossible to distinguish leftover junk on the screen from the
data stream you wish to view.

I believe this bug exists in 6.0 also.