Update documentation to fix #672.

src/mlpack/methods/neighbor_search/neighbor_search.hpp

@@ -219,6 +219,11 @@ class NeighborSearch
    * number of points in the query dataset and k is the number of neighbors
    * being searched for.
    *
+   * Note that if you are calling Search() multiple times with a single query
+   * tree, you need to reset the bounds in the statistic of each query node,
+   * otherwise the result may be wrong!  You can do this by calling
+   * TreeType::Stat()::Reset() on each node in the query tree.
+   *
    * @param queryTree Tree built on query points.
    * @param k Number of neighbors to search for.
    * @param neighbors Matrix storing lists of neighbors for each query point.