diff --git a/ompi/mca/pml/csum/pml_csum.c b/ompi/mca/pml/csum/pml_csum.c
index d67848de87..308fcc49c7 100644
--- a/ompi/mca/pml/csum/pml_csum.c
+++ b/ompi/mca/pml/csum/pml_csum.c
@@ -428,6 +428,12 @@ static void mca_pml_csum_fin_completion( mca_btl_base_module_t* btl,
     MCA_PML_CSUM_PROGRESS_PENDING(bml_btl);
 }
 
+/**
+ * Send an FIN to the peer. If we fail to send this ack (no more available
+ * fragments or the send failed) this function automatically add the FIN
+ * to the list of pending FIN, Which guarantee that the FIN will be sent
+ * later.
+ */
 int mca_pml_csum_send_fin( ompi_proc_t* proc,
                           mca_bml_base_btl_t* bml_btl,
                           void *hdr_des,
@@ -500,7 +506,7 @@ void mca_pml_csum_process_pending_packets(mca_bml_base_btl_t* bml_btl)
         if(NULL == send_dst) {
             OPAL_THREAD_LOCK(&mca_pml_csum.lock);
             opal_list_append(&mca_pml_csum.pckt_pending,
-                    (opal_list_item_t*)pckt);
+                            (opal_list_item_t*)pckt);
             OPAL_THREAD_UNLOCK(&mca_pml_csum.lock);
             continue;
         }
@@ -513,12 +519,11 @@ void mca_pml_csum_process_pending_packets(mca_bml_base_btl_t* bml_btl)
                         pckt->hdr.hdr_ack.hdr_dst_req.pval,
                         pckt->hdr.hdr_ack.hdr_send_offset,
                         pckt->hdr.hdr_common.hdr_flags & MCA_PML_CSUM_HDR_FLAGS_NORDMA);
-                MCA_PML_CSUM_PCKT_PENDING_RETURN(pckt);
-                if(OMPI_ERR_OUT_OF_RESOURCE == rc) {
-                    MCA_PML_CSUM_ADD_ACK_TO_PENDING(pckt->proc,
-                            pckt->hdr.hdr_ack.hdr_src_req.lval,
-                            pckt->hdr.hdr_ack.hdr_dst_req.pval,
-                            pckt->hdr.hdr_ack.hdr_send_offset);
+                if( OPAL_UNLIKELY(OMPI_ERR_OUT_OF_RESOURCE == rc) ) {
+                    OPAL_THREAD_LOCK(&mca_pml_csum.lock);
+                    opal_list_append(&mca_pml_csum.pckt_pending,
+                                     (opal_list_item_t*)pckt);
+                    OPAL_THREAD_UNLOCK(&mca_pml_csum.lock);
                     return;
                 }
                 break;
@@ -527,15 +532,17 @@ void mca_pml_csum_process_pending_packets(mca_bml_base_btl_t* bml_btl)
                                           pckt->hdr.hdr_fin.hdr_des.pval,
                                           pckt->order,
                                           pckt->hdr.hdr_fin.hdr_fail);
-                MCA_PML_CSUM_PCKT_PENDING_RETURN(pckt);
-                if(OMPI_ERR_OUT_OF_RESOURCE == rc)
-                     return;
+                if( OPAL_UNLIKELY(OMPI_ERR_OUT_OF_RESOURCE == rc) ) {
+                    return;
+                }
                 break;
             default:
                 opal_output(0, "[%s:%d] wrong header type\n",
-                        __FILE__, __LINE__);
+                            __FILE__, __LINE__);
                 break;
         }
+        /* We're done with this packet, return it back to the free list */
+        MCA_PML_CSUM_PCKT_PENDING_RETURN(pckt);
     }
 }
 
diff --git a/ompi/mca/pml/csum/pml_csum_recvreq.c b/ompi/mca/pml/csum/pml_csum_recvreq.c
index 6aed902251..7e81b71129 100644
--- a/ompi/mca/pml/csum/pml_csum_recvreq.c
+++ b/ompi/mca/pml/csum/pml_csum_recvreq.c
@@ -227,7 +227,7 @@ int mca_pml_csum_recv_request_ack_send_btl(
     /* allocate descriptor */
     mca_bml_base_alloc(bml_btl, &des, MCA_BTL_NO_ORDER,
                        sizeof(mca_pml_csum_ack_hdr_t),
-                       MCA_BTL_DES_FLAGS_PRIORITY | MCA_BTL_DES_FLAGS_BTL_OWNERSHIP);
+                       MCA_BTL_DES_FLAGS_PRIORITY | MCA_BTL_DES_FLAGS_BTL_OWNERSHIP | MCA_BTL_DES_SEND_ALWAYS_CALLBACK);
     if( OPAL_UNLIKELY(NULL == des) ) {
         return OMPI_ERR_OUT_OF_RESOURCE; 
     }
@@ -252,9 +252,6 @@ int mca_pml_csum_recv_request_ack_send_btl(
 
     rc = mca_bml_base_send(bml_btl, des, MCA_PML_CSUM_HDR_TYPE_ACK);
     if( OPAL_LIKELY( rc >= 0 ) ) {
-        if( OPAL_LIKELY( 1 == rc ) ) {
-            MCA_PML_CSUM_PROGRESS_PENDING(bml_btl);
-        }
         return OMPI_SUCCESS;
     }
     mca_bml_base_free(bml_btl, des);
@@ -381,7 +378,7 @@ int mca_pml_csum_recv_request_get_frag( mca_pml_csum_rdma_frag_t* frag )
                               MCA_BTL_NO_ORDER,
                               0,
                               &frag->rdma_length,
-                              MCA_BTL_DES_FLAGS_BTL_OWNERSHIP,
+                              0,  /* always call the callback, PML ownership */ 
                               &descriptor );
     if( OPAL_UNLIKELY(NULL == descriptor) ) {
         frag->rdma_length = save_size;
@@ -831,7 +828,7 @@ int mca_pml_csum_recv_request_schedule_once( mca_pml_csum_recv_request_t* recvre
         }
 
         mca_bml_base_alloc(bml_btl, &ctl, MCA_BTL_NO_ORDER, hdr_size,
-                           MCA_BTL_DES_FLAGS_PRIORITY | MCA_BTL_DES_FLAGS_BTL_OWNERSHIP);
+                           MCA_BTL_DES_FLAGS_PRIORITY | MCA_BTL_DES_FLAGS_BTL_OWNERSHIP | MCA_BTL_DES_SEND_ALWAYS_CALLBACK);
 
         if( OPAL_UNLIKELY(NULL == ctl) ) {
             mca_bml_base_free(bml_btl,dst);
@@ -879,10 +876,6 @@ int mca_pml_csum_recv_request_schedule_once( mca_pml_csum_recv_request_t* recvre
             OPAL_THREAD_ADD_SIZE_T(&recvreq->req_pipeline_depth, 1);
             recvreq->req_rdma[rdma_idx].length -= size;
             bytes_remaining -= size;
-            if( OPAL_LIKELY( 1 == rc ) ) {
-                /* The send is completed, trigger the callback */
-                MCA_PML_CSUM_PROGRESS_PENDING(bml_btl);
-            }
         } else {
             mca_bml_base_free(bml_btl,ctl);
             mca_bml_base_free(bml_btl,dst);