Dependant field appears only after saving

Good afternoon,

I have a field "Sous groupe DDO/AV" that is dependant of the some of the users "Assigned to".
This part is working great.

So when I, as an administrator, choose one of the users who will triger the dependency, the field "Sous groupe DDO/AV" appears directly.
However, if a basic user does the same, the field will not show. He needs to save the case, come back to it, then the field "Sous groupe DDO/AV" will be available.

Do you guys know why this difference ? Something i can change ?

Thanks !