Symptoms

Values added to fields during the quick-create subtask do not appear in the created task.

Cause

The quick add sub-task screen doesn't belong to JIRA as a screen. It only links displayed fields to the default create issue screen.

In this case, the fields that its values are not configured correctly also are not present in default create issue screen.

Resolution

Add all fields showed on quick add sub-task to default create issue screen.