I would guess that one of TMQFORWARDS "clients" is actually aborting a transaction (and possibly also generating a message for the REPLYQ). When the transaction is aborted TMQFORWARD is (depending on the retry configuration for the queue) often supposed to make another try.
I don't know the workings of the qsample app but it would be reasonable to assume that a transaction abort would be part of the scenario.
Maybe you should run the application with TMTRACE=on in the environment. This will show you (in the ULOG) what goes on wrt transactions and other things.
Hope this helps,