I'm using LMDE UP 5 with MATE.
I played around with the workspaces widget for a bit and decided to try something new: instead of 5 workspaces in one row, I wanted to try 20 (or 16? I don't exactly remember) workspaces in two rows.
Then I continued working as usual when suddenly the processor load went up to 100% and the window borders (i.e., window title, minimize / maximize / close buttons) of all visible programs disappeared. Other symptoms: Grabbing a window by pressing Alt and left mouse button, and resizing a window by dragging its corner are impossible.
I suspected the workspaces to be the cause and tried to cut their number down again, but I can't because the workspaces settings window gets glued to the upper left corner of the screen and the upper half of it is missing completely (no list of workspaces, no "set number of workspaces" slider etc.).
Relogin/reboot did nothing to solve this.
My problem is similar to the one in this thread: window manager goes off in LMDE 13 with compiz, but I decided to open a new thread because my problem has nothing to do with Compiz (at least it seems that way to me?). The screenshot in that thread totally fits my issue.
I'm writing this post using Cinnamon where the window borders are visible and behave as expected, but I prefer MATE and would really like it if MATE worked the way it did before.
Please help me.