Apparently, this was one of either my domain_create_post.sh or domain_destroy_post.sh scripts. Both of them open /usr/sbin/sendmail and send me an email upon domain deletion/creation.
Somehow this broke the user creation/deletion function of the new DA build. If I recall, they worked fine with version 1.21.2. I can still add/remove domains, and the script works fine for that, but it hangs DA on user creation/deletion.
Any ideas? I can email you the scripts, if you like.