LDAP and CommandByMail Incompatible?

I went through the installation instructions for CommandByMail (0.05) and
got that working well. I then went through the installation instructions
for LDAP to connect RT to our Active Directory. I am able to successfully
authenticate to RT as an AD user, and I see the full AD account details in
the log file during a login so I know that LDAP integration is working.

But I stopped receiving emails from the RT system, and sending an email to
it started bouncing with “Could not load a valid user”. I could watch the
email through the mail system all the way to the rt-mailgate call, and the
logs didn’t show any abnormal messages, but still no correspondence. If I
disable the CommandByMail extension in the config file, emails flow in both
directions as expected.

Does anyone have both the LDAP integration and CommandByMail extension
working in the same RT installation? If so, did you have to do anything
special to get the email to work?