If I open an app (say apple music) in tabbed mode it generates a new tab in tabbed view. when I hide this app the tab is removed and the app enters "hidden state". So far expected behavior. If I now unide the app by clicking the dock icon the app "hijacks" the current active tab. Selecting another tab and reselecting the "hijacked" tab shows the original app (before hijacking) again. This was tested on Tangrid 1.5.4...
Just another remark: It would be nice to be able to define a default stack that will always grab new windows. If You have more than one tabbed stack on the screen openining in the current active stack is often not what at least I want...