When using datasharing, IDMS can dynamically route database transactions to one of a number of back-end CVs defined in a DBGROUP.
This is documented at Using Dynamic Database Session Routing.
Attempting to use this functionality can result in a 1480 error-status.
Release : All supported releases.
Define the DBGROUP to the front-end CV as well (IDMS050 in the example on TechDocs linked above), and if you specifically want the transactions in the dbgroup to not be able to run in that CV, issue DCMT VARY DBGROUP EMPGROUP LEAVE on IDMS050.