Able to Assign User beside Agents for Issue that is created through JIRA Channel

Steps to Reproduce:

1. Create a service desk project.
2. Go to the Project's Administration > Role.
3. Include a user who is not an agent to the "Service Desk Team" role e.g. User A.
4. Create a new issue for that project through JIRA not Service Desk.
5. Assign the issue to User A on the creation.

Expected Result:
The issue is created and assigned to User A.

Actual Result:
The issue is not created as User A is not eligible to be assigned even though the issue is created through JIRA Channel.