We do have a custom email_change_pass_post.sh set, but the script runs fine. If we change the password within DirectAdmin it shows an "Account password changed" message, only /CMD_CHANGE_EMAIL_PASSWORD shows a blank page on success. The script does not, and cannot, return anything or DirectAdmin will think the script failed.
Ownership of the file is correct:
-rwx------ 1 diradmin diradmin 608 Jun 30 11:04 email_change_pass_post.sh
Removing/renaming the script result in the /CMD_CHANGE_EMAIL_PASSWORD show "Password Saved!" again.
P.S. Emailed support about this problem.