Hmm. After returning to the problem a week later, I can't reproduce my own results.

I'm getting the behaviour I stated for the 5.1.2 server, but not for the 6.0.3 any more. (I think perhaps I just got confused between the various test cases I'm cycling through.)

I understand that you are no longer "officially" supporting 5.x servers anymore, however our overcomplicated server structure will make it a difficult task to upgrade.

I believe you should be able to reproduce this issue using a 5.1.2 server and I've uploaded a test case which you can run. It should be exactly the same as your test except a slightly older version of Lightstreamer.

If you can reproduce this in any way at all, even using an outdated server, it will make me happy.

It may be that between the sniff and the Lightstreamer server there is some software component such as antivirus, firewall or similar?
Ever since I understood that the <use_enriched...> flag was involved, I've been able to reproduce the scenario using localhost:8080 like you. I'm not really using my remote test server anymore. So I believe I've removed this possibility.