Upgrading MongoDB ReplicaSet to 3.0 causes BSONElement: bad type 108

I followed the official guide to upgrade a MongoDB ReplicaSet from 2.6 to 3.0 on the secondary member.

1. Shutdown mongod (systemctl stop mongodb.service) on secondary
2. Installed binaries (via apt-get)
3. Update mongod.conf
4. Restart mongod: failed!

[NetworkInterfaceASIO-Replication-0] Uncaught exception in NetworkInterfaceASIO IO worker thread of type: Location10320: BSONElement: bad type 108

[NetworkInterfaceASIO-Replication-0] Fatal Assertion 28820

Looks like my databases are corrupt but mongod w/out replSet works fine with the same dbs.

Did I miss something?