It is also possible to create the middle domain via LDAP commands only. Something like the following should work:
modify this entry:
The zimbraId should be globally unique. Using the above should be fine.
create this entry:
That is all that is needed to turn the existing "dc=abc,dc=com" entry into a recognized Zimbra domain. You'll probably need to restart tomcat as well.
The bug is fixed in the next release.