Synfig Docked Dialogs Bug

I have a bunch of dialogs all docked together in the left pane, and the 'layers' dialog on its own in the right pane:

I drag the border separating the two panes to the left:

As you can see, the icons along the top of the left pane aren't hidden as you might expect them to be.

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dooglus > synfig > docked dialogs bug