Mirroring Dummy only temorarily flashes up mirror display the reverts

[timboxyz]

Using 1.12 on Monterey 12.3.1 and have set up a 1920x1080 dummy.
When I try and mirror this onto a genuine external 1920x1080 monitor the displays blink. Temporarily show the correct mirroring, but then revert.

If I use the System Preferences mirroring it seems to work OK.

[waydabber]

Sometimes this does happen, unfortunately display and mirroring configuration is not an exact science in macOS (should be but the windowserver does its own things. Resetting the display configuration usually helps (#191 (comment)) but if you were able to set up mirroring using System Preferences and it is stable I would not bother resetting everything. :)