• Start creating new work, enter all required fields.
• In the drop-down list "work attributes" choose "key", but do not enter any value.
• Click the button "enter edit".

The editing interface remains active (the edit is not saved), there is no error message. A user has to guess what is wrong. Obviously the key value is mandatory if the "key" is chosen from the drop-down list, but there is no indication in the GUI.

I was distracted for a couple of minutes when I was entering a new work, and after returning I forgot to enter the key value. Without any error message I lost time searching what is wrong. It would be much easier if an appropriate error message will be displayed.