Changing command default attempt throws error

I duplicated command object WRKOBJPDM to a new command SRCIN in my library.

I then attempted to run:
CHGCMDDFT CMD(SRCIN) NEWDFT('OBJTYPE(*FILE) OBJATR(''*SRC*'')')

But this gives error CPF6260:

Message . . : Errors detected while changing defaults.
Cause . . . : One or more errors were detected while changing
the default values for command WRKOBJPDM in library QPDA.
Recovery . : See the previously listed messages. Correct the
errors and then try the command again.

There are no "previously listed messages". FWIW, job logging is: LOG(4 00
*SECLVL)

I find it interesting that it thinks I'm changing the QPDA/WRKOBJPDM
command object rather than the one I specified.

I've done this exact same thing in several previous shops without any
problems. We're on v7r1.

Any ideas?

- Dan