Hidden scratchpad workspaces can end up being mapped to a screen and cause flicker

[greweln]

Describe the bug

Switching between scratchpads on the same screen causes screen flickering.
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[sminez]

I think I've managed to hit something similar to this but when opening an image viewer while a scratchpad is present. In my case the flickering seems to be thanks to the scratchpad workspace somehow getting placed on the screen directly which definitely shouldn't be happening.

I suspect that what you were hitting @greweln is the same issue: moving a scratchpad to the hidden workspace and then somehow the scratchpad window retaining focus so that workspace gets pulled to the screen before the new scratchpad gets focused (rinse and repeat at an uncomfortable rate). I'll update the issue title now that I have an idea of what to look at.