Maybe that squat rack that you used was wider. The closer the supports to the plates, the less leverage there will be to catapult the bar. The squareness was a coincidence.
Also, if you pull the weight off one side, but the other side's plates are shoved up against the pin, you have less leverage.
All that being said, part of the Max Fat Loss Plan is walking back and forth, evenly removing the plates.

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Lost Dog's Blog & Workout Log
Superman never made any money
saving the world from Solomon Grundy
and sometimes I despair the world will never see
another man like him
-Crash Test Dummies. "Superman's Song"