Editor mode tabs can get corrupted in the layout

This can happen with any mode.

What actually happens is, when closing the Editor, the Editor saves its layout before closing the active Editor Mode, which leads the editor to think the tabs are still opened in the next session.

You can see that in the files : "APPDATA/Local/UnrealEngine/Editor/EditorLayout.json" and "APPDATA/Local/UnrealEngine/Editor/5.3/Saved/Config/WindowsEditor/EditorLayout..ini"

When opening the same Editor Mode again, the editor will :

• try to open the tab again
• find the tabstack where it was saved in the layout
• fail to find a closed tab of teh same id in that tabstack (as it is labeled as "OpenedTab")
• Open a new at that position which will register the tab a second time in the same tabstack

 

This leads to the tab to always open in the initial tabstack because the tabstack will always contain at least one entry corresponding to our tab, even if we move the tab to another tabstack.

Some exceptions to this behaviour exists, but you'll find it pretty easy to reproduce (especially if you reproduce exactly the steps I made in the videos).

Moreover, if you reproduce the bug again (closing the Editor while the Editor Mode is active), you will notice that the tab is registered twice or more in the layout, and even in the same tabstack.

 

In terms of code, the reason all of this is happening is FGlobalTabmanager::SaveAllVisualState() is called before FAssetEditorModeUILayer::OnToolkitHostShutdownUI().broadcast()

My temporary solution (which is far from ideal) is to call GLevelEditorModeTools().DeactivateAllModes() before the layout is saved

1. Launch the editor and open animation mode
2. Close the editor using the "x" button on the top right without exiting animation mode
3. Re-launch the editor and enter animation mode again
4. Move any of the animation mode tabs to a different location (e.g move the Anim Outliner to be next to the details panel)
5. Exit and re-enter animation mode

Expected: The new position of the tab you moved is remembered

Actual: The tab you moved is placed back in it's original position