[once more, please keep wireshark-bugs mailing list in copy, thanks]
As I already explained in my previous message, the reassembly API expects the frag_number parameter to start from 0 for the first fragment of a given message and increase by 1 for each new fragment of the same message. If you apply this rule it will just work.
I don't know why you stopped using morefrag (which was perfectly fine) but if your messages always have up to 3 fragments you could use the message type as frag_number. If you can have several Continue packets for the same message, then you need to find another way to provide the frag_number parameter.
Best regards,
Pascal.