assign user to work or holiday plan does not work

[Spiros Netos]

 I have made my own work and holidays plans and assigned myself and someone else from the team on them. Each time I save the users assigned and the plan. As long as I stay on the same view, when I click on "assign users" button, I see that they users are assigned indeed. As soon as I leave this view and then come back to it, the assigned users are not there anymore when I click the assign users button.