Why does DB2 Reorg abend with SYSTEM=04E

Why is DB2 Reorg failing to extend and abend with SYSTEM=04E USER=0000

DB2 was requesting an extend for an amount up to the "high allocated RBA".
This appears to be something unique for DB2.
 
In the  &VAMENVIR = 'EOV_VSAM'  an ASR statement was doing:  SET &PDC = &SDC
 
This would reduce the size of the extent, but the extend request still worked.
But DB2 experienced a problem because the extent size was not up to the "high allocated RBA".

The IBM symptom that will be displayed for this problem is ‘MMRC=256’ in the ‘DSNP011I’ message.
 
To avoid this problem, the following ASR statements and logic must not be performed on, or change
the &PDC value for the DB2 data base manager job names (xxxxDBM1) in the EOV_VSAM environment:
 
 - SET &PDC = &SDC
 - DIF/RTF statement: SET &RB = nn
 - LSPACE logic
 
Please contact CA Technical Support if any questions.