I did a simliar test with 2 session beans (x and y) that has "required" tx attrib, each running in its own jboss instance(and its own machine if that matters). I found out that when x calls y, transaction is NOT propagated from one instance to the other. When I print out the transaction, I found that y always starts a new transaction even though x has one already! (I did this with 2.2.2 and 2.4.1 versions)
So, I believe transaction propagation across multiple jboss servers is something not supported yet or it might be a bug they are not aware of (??)
Anyone knows more about this?