Bit of an odd one for you.

Windows 10 using virtual desktops.

I had a credential prompt up on screen on Desktop 1. Whilst working on Desktop 2 I noticed a button on the desktop, not attached to anything, only to realise it was the DF added title bar button for 'full screen all monitors' from the other desktop.

The second attached image shows the mysterious button floating on the desktop.

When clicked it flipped me back to Desktop 1 and made the credential request page full screen, which is odd as you can't normally do that.

Fairly minor as these things go but thought you'd like to know. I'm away for three weeks so won't respond to any further requests. Feel free to email me if you want more detail, I'll forget about this post entirely by the time I'm back.