Hi Ed,
With the 2600's when using these same rev B GBIC's, have you checked the event log on the switch?
With the 2600's they can dectect a 3rd party GBIC's but will still allow them to function, whereas the 5400's will disale them.
If the event log in the 2600's shows some error then it's likely they are non-genuine. If there is no error then I think you should call HP support to discuss.
Matt