Open different tasks if editor is opened in multiple tabs

We assume the following:
A user has opened the taskoverview in two different tabs of his browser. Both tabs share the same session. In the first window he opens a task, in the second window he tries to open another task. This leads to errors since the taskGuid of ONE opened task is stored in the session.

Simplest solution to this misbehavior: on registering the taskGuid in the session we check for a already registered taskGuid. If this is the case we throw an exception with the following message to the user:
"You tried to open another task, but you have already opened another one in another window. Please press F5 to open the previous one here, or close this message to stay in the Taskoverview."