The undo feature (Ctrl+Z) of the code editor can replace the code from another tab.

[VladiStep]

Describe the bug

The undo history could contain the entire code from the previously opened code tab if you switch between "Decompiled" and "Disassembly" mode tabs.
This happens because DecompiledYet/DisassembledYet is not reset to false on switching between code tabs, and also because the UndoStack is listening for changes even on the document fill stage.

Reproducing steps

1. Open two code tabs.
2. Switch to "Disassembly" tab of the first code tab.
3. Switch to the second code tab.
4. Switch back to "Decompiled" tab.
5. Press Ctrl+Z.

Here's a video which demonstrates the both cases:

bandicam.2023-01-08.21-43-56-866.mp4

Setup Details

1. UTMT version - 3cc23d9