Some tool windows don't disappear when I click away

 I'm having an issue with the Structure tool window.

I have it non-docked, non-floating, non-windowed, like the rest of my tool windows.

With all the other tool windows, e.g. Project, Database, Version Control, when the window is visible and I click away - into the editor normally - then the window disappears.

This can happen immediately a window is visible - except with the Structure tool window.

If I open the Structure tool window from my tab bar, the window sits there stubbornly when i click in the editor. Any other window would disappear immediately.

With the Structure window, I have to click in it first, and then it will disappear automatically when I click away.

Just a slight issue. Can be slightly annoying though.