I'm not sure what is really going on but I have to report this anyway. In the screenshot below, when you put a stack of items into the topmost chest, everything should go to the bottommost chest and the middle one should not receive any items. But in 0.14.1 the middle chest does receive some of items, and the number of those items randomly changes every time you try.

However, if you instead place the topmost chest directly on top of the second hopper (i.e. the one on the left side of the middle chest), all the items in the chest go to the bottommost chest as expected. So this has something to do with hoppers' cooldown counter. I mean, it is as if there were a relatively small chance that the second hopper didn't get suspended by the first hopper pushing items into it. It's like a nondeterminism of a multithreaded program.

This relates to now-fixed MCPE-13417.