When adding members to a replica set the member being added is checked against the existing members for string equality, but not resolved IP.

If a member is inadvertently added with a hostname:port that differs from the existing members but resolves to the same IP:port as one of them, the primary will accept the configuration, but the duplicate host will reject it and stop participating in the replica set.

In a small replica set, this can cause the primary to step down, in which case rs.remove cannot be used to remove the erroneous entry.

If this can be changed to also resolve the hostname and compare IP:port to ensure no members are duplicated, this issue would be prevented.