If your chat gets stuck, just go in and out of the steam menu. IIRC alt-tab fixes it too.
If you are in the steam overlay and hit esc you won't be able to do anything in blockland, this issue is also apparent in Fallout 4.You just have to alt+tab when exiting the overlay.
It's been around for a long time, yes.
Testing the duplicator's Ctrl+X?
That's an easy way to reproduce the problem, yes. Just select some large things and delete them, you'll get this sooner or later.
octTree