Can no longer drag a vertical tab to empty space

Steps to reproduce:
Dragging to the empty space in the vertical tab sidebar

Expected behavior:
For any tab dragged to the empty space below the tab creation button in vertical tabs to be placed at the bottom of the list.

Orion, OS version; hardware type:
Orion 0.99.111-rc

Image/Video:
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I can't drag the tab to the empty space.
I used to be able to before 0.99.110.3, the bookmarks sidebar and vertical tab merge.

This makes it incredibly hard to bring a tab to the bottom of the list.