Ubuntu / Debian remote desktop problem

Sometimes, it happens that when I want to connect to one of my Debian machines over the vncviewer tool, I just can’t type in the password to unlock the screen.

Usually after the machine had been running for some time. There was no way to get past this, not even trying to switch users. Later I googled a very simple solution – right-click into the password input field. Don’t know why this works, but it happened to me today again and as I was unable to find the forum where I found this solution, it took me some time to remember what the solution was, so I’m writing this down here, just in case I forget again.

I’ve had this trouble with Debian, but I expect it will be the same with Ubuntu.