Docked tool window becomes floating when closed and reopened

We noticed the following behavior:

1. Undock and float tool window A
2. Redock tool window A
3. Close tool window A
4. Serialize and save the layout
5. Load another layout that does not open tool window A
6. Load the saved layout
7. Open tool window A (".Activate")
8. -> tool window A floats; expecation is that it is docked, because it was docked when it was closed

For some reason this problem does only seem to occur when another layout is loaded between closing and opening the tool window.

I could attach a solution that demonstrates the problem if the steps above are not quite clear.

Thanks in advance for any input regarding this issue.

Best Regards,

Daniel