I guess that with the certificate update that came with 1.3.1 the supl.nokia.com certificate was made invalid (both nokia's and google's are known for expiring from time to time..) Which means our N900s don't trust supl.nokia.com, but they still trust supl.google.com. Other Nokias, other certificates -> they may still work OK with supl.nokia.com (at least my E75 does).