It appears to be an intermittent bug (or fixed already?), but when I posted the comment, I tested each of the following 3 scenarios, then after realising it seemed weird, re-tested the first one to make sure it wasn't a one-time thing . Each time, I used down+attack to raise up a rock from the ground, then a neutral attack to push it at the opponent. In each case, the opponent was standing.
P1 and P2 in default start position, P1 attacks.
P2 gets knocked over while being pushed off-screen.
P1 and P2 in default start position, P2 attacks.
P1 gets knocked back and up, and the rock moves past.
P1 and P2 in swapped positions, P1 attacks.
P2 gets knocked back and up, and the rock moves past.
After restarting my PC and trying again today, the previously-repeatable result from the first test is no longer happening, so as I said, either you fixed it already, or it's an intermittent bug? Not sure which.