Any instructions on how to reproduce?

Please make sure you have the 6.1 errata installed, specifically for gnome-libs
and gnome-core.

I have installed the errata since the initial report and the problem still
happens. I am not sure how to reproduce it, it appears to happen pretty much at
random though any sort of vt100 cursor movement codes will increase the
likelihood of it happening.

I have recently upgraded to Nethack 3.3.0 and I finally managed to get it to run
in the GNOME terminal.  At random, I also see a row of ~ while I play the game
in tty mode (I really don't like the X11/tile version).  It seem to occur
particularly when you move from level to level (ie. going up and down the
stairs).  At random a row of "."'s (which represent floor) are replace with
"~"'s.  Also bits of the walls are replaced by letters.  It seems to get worse
if you repeatedly go up and down the stairs.  I have thought that this was a
Nethack problem, but the game seems to be OK if I don't use X (& GNOME).
However is you save the game and return to it later, the random "~"'s and
letters are still there.  Hopefully this is of some help.  I will look at it
again myself.

John

P.S.  I did install the newest version of gnome-core and gnome-lib
P.P.S. Nethack options=tty,DECgraphics etc...

I think this is most likely a termcap issue.