I would think that the only reason for a PF bush to pop out is that its being subjected to some considerable sideways or twisting force .
And this must be fairly continuous, otherwise the bush flex but would stay central.
It would always settle on its neutral position when one end becomes free .
The OEM being bonded can take sideways but the PF relies totally on its small flanges.
I can't believe the motor actually moves a great deal in a sideways direction ?.
& there is a small amount of mis-alignment in the Chassis mount and the Engine bracket on some cars ..
but then I only seen 3 cars but they all have it!
I feel the PF bush has a design flaw, in that PF probably thought the Mount ( from its basic design) only took forces forward and Aft !! .
C.