Timo, I was able to reproduce the issue. Please follow my story with screenshots to to support. All screenshots are from the MacOS minus one which was taken in Win11. The time dates are in the titles for your reference. Also I'd like to reference that I do have both apps set to stop after 1 min absence. Win11 is set to sleep after 2 min. MacOS is set to sleep after 10 min.
My issue seems to be when I activate WorkingHours between MacOS and Win11. I noticed that I've had a couple of days worth of units appearing after synching from yesterday afternoon. This occurred when activating in Win11, see the screenshot for detail
This morning I kept an eye on my units within MacOS. See the screenshot for what is correct tracking
I think the app within Win11 is behaving as you've stated to in your first and only statement here. See the screenshot for details the app had after logging in to Windows.
It appears that the Windows app was left on since last night which is not true because I've used both computers on the same desk. I made sure to end the timer within the MacOS as detailed in the second screenshot this morning.
My tracking was correct this morning in MacOS, logging into Windows and auto synching the apps then made it wrong. See the screenshot for what happened to my tracking in MacOS after logging into Windows
I appreciate your work😄