Center Fuel tank low and loss of longitudinal stability

PMDG Team great work with 737. Profile Descent could use slight work as it sometimes sticks at 300 fpm.I found what I believe to be a bug with this product as it relates to longitudinal stability. I flew with full tanks from Las Vegas to Baltimore Washington and landed with @ 6k lbs in center tank. I taxied off runway after a great rush down to catch ILS and the bird landed with no bounce in autoland.After the "After Landing" checklist complete, I began to roll toward the gate area when all of a sudden the airplane began a violent roll to the left on the ground and continue dto do this without the hope of recovery.On another flight (still LAS to BWI) at a different time, the aircrfat was level and below near Baltimore with lod center tank fuel below 10000 when it suddenly lost control and descended nose down onto an airport taxiway. I do not believe this was a rudder reversal issue like in the real 737 accidents but sure was interesting.Hope you cna pinpoint this for the next patch.Thank you and keep up the good work. -- Shareef