Was riding on minecart towards a farm when another farm loaded into view. The farm uses a redstone clock system with pistons which activate and deactivate redstone elements. Though the entities were loaded, tthey were visibly obscured by the structure of the farm. While obscured, one of the pistons must have become active. It is likely at this moment when the game crashed; stating it did not have entity data for sticky pistons facing south. [Edit] After reviewing the issue again, it seems that the crash only occurs if the player is looking at the pistons when they activate. If they keep the pistons out of view when they activate the game does not crash.

Since this seemed like an unusual issue, in a new world I placed pistons in all positions (except facing down) and orientations to test single instances of moving pistons. I could not reproduce the issue with an suite of pistons.

I am unsure therefore what the actual end issue is, the bug report has been included.