Version 188.8.131.52 is a maintenance release and does not include any functionality delivered by Upgrade Pack 1.
A detailed fixlist is now available:
Lotus Notes Traveler 184.108.40.206 includes all APAR fixes up to and including 220.127.116.11 IF1 in addition to the APARs listed here.
Lotus Traveler 18.104.22.168 does not include features delivered in Lotus Traveler 8.5.3 Upgrade Pack 1 and can not be installed on that release. A separate maintenance delivery will be provided for the Upgrade Pack 1 release.