3.6 and 4.0 documents have the following statement in this section:

For queries of sharded collections, for clusters with the balancer active, secondaries may return stale results with missing or duplicated data because of incomplete or terminated chunk migrations.

However, as per SERVER-5931, this issue was already addressed in versions 3.6 and above, making the above statement invalid. Therefore, I believe the above statement can be removed from the 3.6/4.0 docs.