Created attachment 799974 [details]
screenshot

Description of problem:

When a user delegate a task to any other user then the window will remain open allowing the to take further actions. E.g. press delegate a number of times even though he already delegated. He has also access to tasks functions like start which he should not have. See attached screenshot.

The attached screenshot shows a task in the task list of user 'mary' which was already delegated to a non existent user 'xyz'. User 'mary' has still access to the buttons 'release' and 'start' a task. Pressing one of these will cause a security exception (present in server log)