Filemgr not working with DFSMS SYS% facility

We are currently running z/OS 2.2 with FM Release 13.01.

We use the DFSMS SYS% facility in order to clone our systems.
SYS% allows you to reference the same data set one a different volume.
You can read more about it in the DFSMS Managing Catalogs manual.

For example:

SYS1.PARMLIB is our running / executing environment
This dataset resides on the ‘A' side volume BIBMA1 –where A indicate the A running side

SYSO.PARMLIB is our back up / Old environment
This dataset resides on the ‘B' side volume BIBMB1 –where B indicates the B old side

Using this method, we clone our entire operating system and all of it components making it very easy to implement and back out.
Anyway, occasionally after we build an environment it is necessary to change a member on the non-running side.

All IBM utilities respect this SYS% and you can access a non- running dataset by specifying SYSO (oh) in your JCL:

DSN=SYSO.PARMLIB,DISP=(SHR)….

When we migrated from STARTOOL to FILEMGR we had to change our JCL accordingly.
Part of our build process needs to change a member on the old side.
What happened with FM is it didn't respect the SYS% and actually changed the running environment – which is very dangerous in our case.

I set up the following test to show you the results:

I set up two datasets – this is on the Running side (A side)
Data Set Name . . . : SYS1.MM.TEST
General Data
Volume serial . . . : BOEMA1 <- A side

Data Set Name . . . : SYS1.MM.TEST
General Data
Volume serial . . . : BOEMB1 <- B side

Physically both datasets are SYS1.MM.TEST, however you can reference the second one by specifying
SYSO.MM.TEST (that's SYS oh)

I used this JCL to attempt to update the SYSO side and it updated the running dataset.
Here is the JCL I used:

//FILEMGR EXEC PGM=FMNMAIN
//SYSPRINT DD SYSOUT=*
//SYSMDUMP DD SYSOUT=*
//IDIOFF DD DUMMY
//FMNTSPRT DD SYSOUT=*
//SYSTERM DD SYSOUT=*
//SYSIN DD *
$$FILEM SET HEADERPG=NO,PAGESIZE=60,DATAHDR=NO
$$FILEM SET WIDEPRT=YES,PRTTRANS=ON
$$FILEM FCH ,
$$FILEM MEMBER=TESTNEW,
$$FILEM PACK=ASIS,
$$FILEM DSNIN=SYSO.MM.TEST  SYSO
C C'TEST' C'PROD'
//*