Hi All,
I need help in following case:
I setup custom field QA Assignee. It is a user picker and shows only users in role = QA for particular project and doesn't have default value.
I need this field to be required only when specific transition happens.
I put a validator on this particular transition (Fields Required (JSU))
When I move issue according the transition the custom field appears on screen and it is empty. I fill in the field and on submit an error message appears that this field is required and form can't be submitted even user is selected.

The only way this works is if I open the issue for editing and add user in this custom field. After this I can do a transition without an error.
Is there a way to make such custom field required only on specific transition?