🚀 go-pugleaf

I've been using gnuchess-4.0.pl60/xboard-2.0.pl25 as a chess
learning tool.  I like to use the backward/forward feature of
xboard to try out different move sequences and see how they
play out.  When I'm done playing a sequence, I select "Machine Black"
and continue the game.  I've noticed that when I play like this,
gnuchess sometimes plays very badly.  It selects incorrect moves that
allow it to be checkmated or gives away pieces.  I've saved positions
and loaded them back in to see if gnuchess would make the same
bad moves and it doesn't!  It plays much better from the saved
position than it did the first time around.  What's causing this!?
Why does the use of forward/backword cause gnuchess to select such
bad moves?  I thought position evaluation was a deterministic thing.
Is gnuchess selecting random moves?

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Gary A. Cattelino                  Unocal Corporate Information Services
Phone: (714) 693-6762              5460 E. La Palma Ave.
INTERNET: gary@unocal.COM          Anaheim, CA 92807