I am afraid I am dealing with a much broader issue here.
After your sent me your reply I have created a macro that basically "insert text by typing", just for debugging purposes.
Bug test.kmmacros (2.7 KB)
Pasting or Typing, I have the same issue.
I don't know how to screencast while switching users so I have made a video filming my screen, sorry I have limited technical means to do a good job.
The same issue appears when I VNC or TeamViewer on the account. No matter what accounts is logged in in the front will show impact of the macro running in the background, including the "Action Completed" sound of the macro, which is normally not possible.
It's like Keyboard Maestro is running on a superuser level and get on top of all the logged in user in terms of level of permission.
This is very strange.
I can produce more videos if you want different scenarios.