Confirmation from Apple:

https://developer.apple.com/library/content/technotes/tn2083/_index.html#//apple_ref/doc/uid/DTS10003794-CH1-SUBSECTION52

"""
Many Mac OS X frameworks do not work reliably if you call fork but do not call exec. The only exception is the System framework and, even there, the POSIX standard places severe constraints on what you can do between a fork and an exec.
(...)
Listing 13  Core Foundation complaining about fork-without-exec

The process has forked and you cannot use this CoreFoundation \
functionality safely. You MUST exec().
Break on __THE_PROCESS_HAS_FORKED_AND_YOU_CANNOT_USE_THIS_\
COREFOUNDATION_FUNCTIONALITY___YOU_MUST_EXEC__() to debug.
"""