That variable listed in the subject line is (apparently) the default in the configuration section under the registration tab. The Welcome Email and the Pending Registration email both have that variable inserted.
The correct variable is [DETAILS] but there is nowhere that I could find which listed that fact. I figured it out using trial and (lots) of error. Although it doesn't prevent the email from being sent, it also doesn't provide the proper information.
Perhaps it can be adjusted to be correct and/or mentioned in the insanely huge user manual.
Thanks,
Mark