This test does:

1. start a 3-node set
2. configure key files on nodes 1 and 2 so node 0 gets auth errors in replSetHeartbeat
3. confirm node 0 goes into RECOVERING due to auth errs (SERVER-3715)
4. stop nodes 1 and 2
5. confirm node 0 goes into SECONDARY
6. restart nodes 1 and 2
7. stop node 0 <-- BF
8. more test operations....

Rarely, after nodes 1 and 2 are restarted in step 6, node 0 has time to heartbeat another node, get an auth error, and go from SECONDARY back to RECOVERING. As a result, when ReplSetTest tries to stop node 0 in step 7, it fails, because ReplSetTest's procedure for stopping a node includes validating collections, which does not work on a RECOVERING node.

If we stop node 0 before restarting nodes 1 and 2 that should fix the race.

I believe the test has had this bug since it was first written for MongoDB 2.2 and backported to 2.0.