Steps to reproduce:
1. Scroll a flickable with the finger until it an edge, and scroll it even further until it is clearly out of bounds.
2. Release the finger so the rebound transition starts.
3. Very quickly, before the transition finishes, grab the flickable with the finger (don't move the finger yet). Now the result is different depending on whether there is a custom "rebound" transition or not:
3.1 Without a custom rebound transition, the rebound animation will continue until the end.
3.2 With a custom rebound transition, the rebound animation stops (as expected) and the flickable is still under the finger keeping the out of bounds offset.
4. Move your finger. As soon as you do this, the flickable will jump to a position that seems to be the size of exactly one item out of bounds in a ListView. This will happen both after scenario 3.1 and 3.2. The expected outcome is that the flickable does not jump, but it continues moving from the position where it was grabbed.