Hello Karel,
I was able to recreate the issue you are having with the same script that I copied above in version 15.0.3 ESD 1.
Looks to be a version issue after all.
Checking master: Logical pagesize is 2048 bytes
DBCC CHECKSTORAGE for database 'master' encountered an error. Some results may not be available. Correct the problems reported and reexecute the CHECKSTORAGE command.
Number (9965) Severity (20) State (1) Server (testserver) Procedure (sp__dbcc_db_pubs) The entries in dbcc_config for database 'master' are either missing or invalid. Use sp_dbcc_evaluatedb to determine appropriate values for the entries and sp_dbcc_updateconfig to set them.
This works without rpc.
Let me know how you fare with 15.7.
warm regards,
sudhir