When composing a post (for example this one that I’m composing right now), I can maximise the editing window with the angled double-arrow at the top right.

When I do this, however, the plus-sign in the toolbar doesn’t work.
Here’s what it looks like in normal mode, when it works:
But, in maximised mode, it appears to do nothing when I click the plus-sign.
The same happens when I select the “Close” button at the bottom. It should ask me whether I want to Discard, Save draft for later, or Keep editing, but nothing appears to happen. What actually happens is that the dialogue is displayed behind the maximised window, and becomes visible if you restore the editing window to its normal size.
It seems that the dialogues have a lower display (z-axis) priority than the maximised editing window.
My normal browser is Chrome. I’ve tried using a different browser, specifically Firefox, and that did the same.

