10RC1 crash testing MultiXact oddity

I am running some crash recovery testing against 10rc1 by injecting torn
page writes, using a test case which generates a lot of multixact, some
naturally by doing a lot fk updates, but most artificially by calling
the pg_burn_multixact function from one of the attached patches.

In 22 hours of running I got 12 instances were messages like this appear:

MultiXact member wraparound protections are disabled because oldest
checkpointed MultiXact 681012168 does not exist on disk

This is not a fatal error, and no inconsistent data is found at the end of
the run. But the code comments suggests that this should only happen on a
server that has been upgraded from 9.3 or 9.4, which this server has not
been.

Is the presence of this log message something that needs to be investigated
further?

Thanks,

Jeff