Today we have been successful in solving the oldest bug of eCAD. This bug was about the MDI implementation. If multiple documents have been created in eCAD, you can only work on the latest one. All the previous documents were unresponsive.
So we used a signal that is emitted whenever MDI subWindow is changed or created.
And we connected this slot to a function that then updates the pointer of the graphicsview to the corresponding subWindow.
This solves the issue and every document can be accessed now.
Now we can solve other issues related to this as well like respective menu items and shortcut keys.