Undoing subdiagram extraction does not always work

[RainerKlute]

I observed this at least twice, but haven't been able to reproduce the exact conditions. Anyway, at least here is one path to reproduce the faulty behaviour; there might be more.

1. Extract the subdiagram.
2. Click on the decorator (twice, see issue No subdiagram editor on click immediately after creation #1536). The subdiagram editor opens.
3. Close the subdiagram editor (without saving).
4. Press [Ctrl+Z] or select Edit → Undo Refactoring Command. Nothing happens.

[BeckmaR]

Related to:

• Redo doesn't work after refactoring #1137
• Undo doesn't work with "Refactor -> Extract subdiagram" #803

[BeckmaR]

Actually, exact duplicate of #1137