yes, Toolbar in my post correspond to Windows TaskBar . Sorry to not using correct term.
On My PC the taskbar is on right border of screen.
To be precise, I distinct 4 cases
1. draging over right border of taskbar
2. draging over left border of taskbar
3. draging over taskbar
4. draging after left border
If I drag over right border and remain there 1 or 2 second, the fences is moved to the left page.
If I drag over taskbar, nothing happen
If I drag over left border of taskbar that is equivalent to left border of screen, nothing happen
If I drag more to the left, fences is moved to a new tab.
That is what I have experimented.
In fact, the first time I have dragged the Fences to the left. The mouse has certainly be over the right border of taskbar but to quickly so that program react and move Fences to left page.
I have then continues to drag the Fences more to the left.
Draging over Taskbar make nothing.
Draging over left border of taskbar make nothing.
Continue to drag more to the left move Fences to a new page.
That is what I have seen.
I hope that you can understand that this is a little disturbing to see that you try to move a Fences to the page just to the left and that suddenly the Fences has been moved to a new tab at the right ! 
Thats is why I find this feature bizarre/weird and not very natural for human.
This is just my personal opinion.