Undo / redo does not work across tabs

[Tim Krieger]

Steps to reproduce:

1. Create a mind map »test1« with two branches.
2. Create a second mind map »test2« with three branches.
3. Change to »test1« and undo the last changes.

Result:
»test1« is renamed to »test2« (with three branches).

Chromium (Linux), Safari (iOS)

[Cedoor]

Yes I know it, I have to correctly set mmp to create multiple instances, one for each tab. At the moment the instance is the same and the tabs are managed with the mmp history. Thanks!