To follow up on this I have created a JMeter script that exposes this problem.
The script simply hits the clusterjsp page, adds some session data and then toggles between the two instances making sure the session data is present.
Using a "Constant Throughput Timer" I set the request rate to less than 400req/min and it works fine. If I increase the throughput to over 1000req/min then a few requests succeed before the session is lost and it starts failing.
This behaviour occurs with V2UR2 and V2.1 b45.
In my opinion this is a pretty serious problem!
I have attached the JMeter test script for your convenience. You can change the hostname and port numbers in the user parameters section at the top if required. The default is localhost and ports 38080 and 38081.
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