Hi Coral,
1. If the logged in user has the AssignAnyJob privilege, there is no way to restrict the assignment based on what group the job is currently assigned to. However, if a user only has the GroupJobAssign privilege, they will only be able to assign it to other members of the groups they belong to. This may accomplish the same result that you desire.
2. This sounds like it might be an issue with the job query, as only 1 job is ever created with the same ID. The query may have an improper join to the JTX_USERS table and is showing the same job for each record in the table. Was this query created with the SQL Builder? If so, can you try removing the JTX_USERS table from the FROM section of the query (as well as any fields from this table from the SELECT section) and see if it resolves the issue?
Kevin