Comment by wpollock

Your post reminded me when Yahoo IM updated their chat protocol to an incompatible version with a gradual rollout! Half their eight servers used v1 and half v2. A v1 only client would connect half the time depending on which server the round-robin DNS sent you to. This took me forever to figure out, but the fix was to put the IP address of the four v1 servers in the hosts file. (Until the client updated its support for v2.)