I Just re-read the question; I didn't realize they were on the spring on the same time
On first read I got the impression that the objects were tested on the spring separately hence my confusion
"It's because the objects will fly off of whatever platform is accelerating them upward as soon as the acceleration of the platform becomes greater than g in a downward direction. So the criterion for flying off is independent of mass. "
I am having a similar problem as the OP. How do you...