Please, anyone, I need help.
Data gravitation takes place on a per-node level (and by node, I mean a node in the cache's tree structure such as /testRegion). Since both servers in your case (what you call NodeA and NodeB) are putting things in the same tree node in the cache (/testRegion) you have a problem.
Each server should use a different FQN such as /testRegion/ServerA and /testRegion/ServerB
Also, if you have only 2 servers, don't waste your time with buddy replication - you will find that total, synchronous replication is more efficient. The benefits of BR is only seen in larger clusters.