Oliver,
Client transaction propagation from Client and Server should work. I have couple of questions. Are you running your client in the Application Client Container or running as a stand alone Container?
You don't seem to be using customersEmf and productsEmf in the client? Is that assumption correct?
Can you get the jstack output of the client when it is hanging and server.log when JTS and JTS log levels are set to FINE?
Could you also please try looking up explicitly UserTransaction, instead of injecting (not that it should matter).
regards
sankar
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