I think I'm onto something:
The Assembler module establishes a VSAM ACB and buffer space for VSAM and establishes a VSAM Journal exit.
THe Assembler module calls the COBOL module that loads into it's own LE Enclave.
The COBOL module opens it own VSAM ACB (OK, it does know any better).
THe COBOL program does a read key on the VSAM file.
This drives the exit which accesses the ACB in the Assembler enclave which hasn't been used.... S0C4?