The syslog only appears to log successful successful logins to the TPAM interfaces, failed login attempts and not sent to syslog.
These are not currently captured because they are not an activity in TPAM. We do, however, record the failures in the Failed Logins report (/par or /tpam interface | Reports | Audit Reports | Failed Logins).
Issue fixed in version 2.5.913. The latest version of TPAM can be downloaded here