When activating Zend mode, there's a message displayed for the user to alert about this and the user can close that message clicking on the red cross.
One issue is that if the user do not close that message, when he closes Zend mode (by clicking the arrow on the top right) and clicking it again, the message is duplicated. Everytime the user activates Zend mode, the info message is duplicated
The other issue is that when the message is not closed and Zend mode is deactivated, the message remains displayed.
I think this is a regression from creating an angular directive for notifications. Should be fixed now.
When closing Zen mode a not previously closed message will still stay. This was never implemented but could be done. So will leave the ticket open
Fixed in master, forgot to close.