Undo/redo buttons can be in an incorrect state in the Sanger Reads Editor

Scenario to reproduce:

1. Open a Sanger reads alignment.
2. Edit it.
3. Close the view.
4. Open the view again.
   Expected state: the undo and redo buttons are enabled, if there are actions you can undo or redo.

This issue can appear irregularly.
Check, that everything is ok, if you unload the document, remove the document from the project, close the project, close the application etc.