Per https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/256, we need

to set *flag=1 when source == MPI_PROC_NULL.

cmr:v1.7.2:reviewer=dgoodell
cmr:v1.6.5:reviewer=dgoodell

This commit was SVN r28621.

ompi/mpi/c/iprobe.c

@@ -61,6 +61,7 @@ int MPI_Iprobe(int source, int tag, MPI_Comm comm, int *flag, MPI_Status *status
     }
 
     if (MPI_PROC_NULL == source) {
+        *flag = 1;
         if (MPI_STATUS_IGNORE != status) {
             *status = ompi_request_empty.req_status;
             /*