Symptoms

When trying to create a sub-task from Crucible the assignee field is ignored.

Cause

This can be caused due to many reasons:

1. You have removed the assignee field from the create issue screens.
2. If you are authenticating with a username and password, who does not have assign issue permission.
3. If you are authenticating with trusted applications, the logged in Crucible user does not have assign issue permission.
4. There is a workflow post function that is assigning the issue to the default user

Resolution

Case 1: Ensure that the assignee field is included on the create issue screen.
Case 2 & 3: Ensure that the user has created issue permission.
Case 4: Unfortunately you will need to remove the post function as it is incompatible with the feature.

There may be other causes, in which contact Atlassian Support.