If a node is replaced with -Dcassandra.replace_address, the new node has mostly null entries in system.peers:
To reproduce, simply kill a node and replace it. The entries are correctly populated if the replacement node is restarted but they are never populated if it isn't.
I can think of at least two bad consequences of this:
1. Drivers like Datastax java-driver use the peers table to find the rpc_address and location info of a node. If the entires are null it assumes rpc_address=ip and the node is in the local DC.
2. When using GossipingPropertyFileSnitch and node won't persist the DC/rack of another node so may not be able to locate it during restarts.
I reproduced in 1.2.15 but from inspection it looks to be present in 1.2.16 and 2.0.7.