equal load balancing in multi tier senario :

OK, very odd behaviour. A few more questions;

1. Do the clients use a proxy?
2. Any NTLM involved?
3. Does the Persistence profile have any 'Match Across' options configured?
4. Are the real servers in any other Pools?
5. Are the Pool Members actually different servers, or the same but listening on different ports?
6. I assume health monitors show all the members as up?