Tab unload resets indent of its first child

[Gotolei]

(Forcing unload through BarTab Heavy, though I've heard of it affecting UnloadTab users as well)

Before unload: https://i.imgur.com/TFSiL9C.png After: https://i.imgur.com/DzU9Uig.png

Only seems to happen if the parent tab is level 0 and the child is level 1.

Firefox 45.0, Linux