This is a regression since 4.7.1.

When you click a Flickable and start dragging, there's a short distance where it doesn't respond, after which it starts to follow the mouse (it jumped to the mouse in 4.7.0, but that was fixed in 4.7.1). This is good.

On the current 4.7 branch leading to 4.7.2, the behavior is broken when you drag the mouse back to where you started from. There seems to be a distance the same (or at least related to) the "start drag distance" where the Flickable contents stop following the mouse, after which it jumps (snaps) to the mouse again. This causes dragging a Flickable to look non-smooth.

The issue can be reproduced with the attached example.