QtC: Undo redo issues
'Steps to reproduce:
- Open a project with 2 .msc files
- Edit the name of an instance in the first file to "AAA"
- Edit the name of an instance in the second file to "BBB"
- Edit the name of the instance in the first file again this time to "XXX"
- Edit the name of the instance in the second file again this time to "YYY"
- Go to the first file and press undo
-> the instance name is set to the original. Expected would be "AAA"