Had a look at you video. It seems it is a matter of UX expectation at my side. What I did is drag the caption bar of the fence down to the taskbar, expecting it to roll up and snap. Now, I see it is the bottom of the fence that is snapping. So, what happened my first time is that I happened to drag the fence caption bar below the Taskbar and release the mouse button, not noticing any snapping behaviour of the caption bar as I expected.
I expected the snap behaviour to be triggered by the caption bar, as that is how it works in Windows.
Cannot say that the snapping behaviour of the bottom of the fence is that clear. I would suggest a (stronger) snapping animation as it comes close to the Taskbar or change the behaviour to conform with Windows.
I feel that in any case it should not be possible to drag a caption bar below the Taskbar, which is really easy in this case.
Hope this clarifies without me figuring out how to do a screen recording in Windows.