The 3.0.x branch implementation of DBCursor.getQuery and DBCursor.getKeysWanted return a copy of the internal property, whereas before they returned a reference to the internal copy. This break clients who do:

DBCursor cursor = collection.find(new BasicDBObject());
cursor.getQuery().put("x", 1);

since because getQuery returns a copy, the put has no effect on the query that's actually performed.

This should be reverted to the previous behavior.