Major - P3 repro script is at https://github.com/10gen/QA/blob/master/QA-404/dumprestore_dbpath.js
just uncomment line 184:
runDumpRestoreTest({s:"2.4",t: "2.4",d: "2.4",r: "2.6", oldSchema:false}, {usersShouldExist:true, loginsShouldWork:true})
this text attempts to start up a 2.4 server (source), another 2.4 server (target), insert a bunch of users in the source, shut down both servers, mongodump from the source and restore into target.
Mongorestore logs this error:
2014-03-17T16:22:38.750-0400 shell: started program mongorestore-2.6 --dbpath /data/db/mongod-50003 sh95626| 2014-03-17T16:22:38.772-0400 dump/admin/system.users.bson sh95626| 2014-03-17T16:22:38.772-0400 going into namespace [admin.system.users] sh95626| Restoring to admin.system.users without dropping. Restored data will be inserted without raising errors; check your server log sh95626| assertion: 17416 Cannot modify user data on a server with version greater than or equal to 2.5.4 that has not yet updated the authorization data to schema version 3. Found server version 2.6.0-rc1 with authorization schema version 1