Redmine

I have set up a workflow, part of which is the status transition:

• Confirmed (field "assignee" read-only and empty) -> Assigned (field "assignee" required),
• Assigned -> Confirmed (same field constraints).

My idea was to restrict Assignee change only in transition to status Assigned. Sometimes developers take issues that are not meant to be taken. We have "Not assigned" project version, "Platform" category and tracker "Info", if either of them is set an issue is considered just for information (subtasks status, etc.), not to be acted upon.

The problem is that I can't unassign them and go back to status Confirmed because when I do that only status changes, Assignee remains set (field disappears after selecting Confirmed status from <select>). In Confirmed status I can't unassign user because field won't show up or Redmine will complain of field being read only.

I think that not unassigning user looks like a bug, but maybe I'm unaware of achieving desired result.