diff --git a/TODO b/TODO
index c14181fa..881a640a 100644
--- a/TODO
+++ b/TODO
@@ -1,5 +1,9 @@
 --- the plan ---
 
+* libreprap:
+	+ don't write anything (particularly a re-send) while
+	  a partial read is underway [?]
+
 * sort out stdafx.h includes - check whether it is
   needed, and where ...
 
@@ -10,9 +14,6 @@
 		+ you need to tweak permissions, or add yourself
 		  to XYZ group, and re-login ...
 
-* Settings re-factor
-	+ stop Model being a widget ...
-
 * Finish the 'Display' settings page
 * add Hardware Settings profiles:
 	+ "Mendel", "XYZ", "etc." ? :-)
@@ -25,14 +26,7 @@
 
 * win32 osc build fun ...
 
---- misc stuff ---
-
-* make toolkit lock sane and truly recursive
-	+ to avoid gdk threads deadlock[!]
-
-* serial
-	+ move ModelViewController DetectComPorts to RepRapSerial ...
-	  ditto ValidateComPort
+--- older stuff ---
 
 * connection button
 	+ should require confirmation before going off-line
@@ -48,17 +42,10 @@
 
 * add click-to-select in the 3D view
 
-* re-factor MVC
-	* rename view.cpp etc. to render.cpp
-		* include SpinRows in view.cpp ...
-	* split chunks of model.cpp to view.cpp etc.
-		* split out / create an 'RFOView' widget to (sanely)
-		  manipulate that treeview
-
 * bug fixing:
 	+ arcball / rotation resetting ...
 	+ re-instate a non-gui mode ...
 
 * add log scrolling:
 	+ gtk_text_view_scroll_to_iter [etc.]
-	+ when the adjustments change etc.
\ No newline at end of file
+	+ when the adjustments change etc.
diff --git a/libraries/libreprap/comms.c b/libraries/libreprap/comms.c
index f5e7cbf6..cce040af 100644
--- a/libraries/libreprap/comms.c
+++ b/libraries/libreprap/comms.c
@@ -89,18 +89,23 @@ rr_dev_pop_from_queue (rr_dev dev, rr_prio priority)
 }
 
 static void
-empty_buffers (rr_dev dev)
+empty_queue (rr_dev dev, int prio)
 {
-  unsigned i;
-  for (i = 0; i < RR_PRIO_ALL_QUEUES; ++i) {
-    while (dev->sendhead[i]) {
-      blocknode *node = rr_dev_pop_from_queue (dev, i);
-      blocknode_free (node);
-    }
-    assert (dev->sendhead[i] == NULL);
-    assert (dev->sendtail[i] == NULL);
-    dev->sendsize[i] = 0;
+  while (dev->sendhead[prio]) {
+    blocknode *node = rr_dev_pop_from_queue (dev, prio);
+    blocknode_free (node);
   }
+  assert (dev->sendhead[prio] == NULL);
+  assert (dev->sendtail[prio] == NULL);
+  dev->sendsize[prio] = 0;
+}
+
+static void
+empty_buffers (rr_dev dev)
+{
+  unsigned int i;
+  for (i = 0; i < RR_PRIO_ALL_QUEUES; ++i)
+    empty_queue (dev, i);
 }
 
 rr_dev
@@ -305,13 +310,6 @@ rr_dev_enqueue_internal (rr_dev dev, rr_prio priority,
   return 0;
 }
 
-/*
- * FIXME - this needs to handle a jump-ahead use-case too ...
- * we can get:
- * rs 2 [and resend N2 ...] followed immediately by rs 6 ...
- * and we need to do the converse - shift lines from the
- * resend queue back onto the sentcache ...
- */
 int
 rr_dev_resend (rr_dev dev, unsigned long lineno, const char *reply, size_t nbytes)
 {
@@ -322,21 +320,43 @@ rr_dev_resend (rr_dev dev, unsigned long lineno, const char *reply, size_t nbyte
   while (1) {
     if (!(node = rr_dev_pop_from_queue (dev, RR_PRIO_SENTCACHE)))
       break;
-    debug_log ((dev, "; pop node line %d '%s' (%d bytes)\n",
+    debug_log ((dev, "; pop sent node line %d '%s' (%d bytes)\n",
 		(int)node->line, node->block, node->blocksize));
     if (node->line >= lineno) {
       rr_dev_prepend_to_queue (dev, RR_PRIO_RESEND, node);
       resent++;
-    } else { /* put it back and exit */
+    } else { /* put it back and look elsewhere */
       rr_dev_prepend_to_queue (dev, RR_PRIO_SENTCACHE, node);
       break;
     }
   }
 
-  if (resent == 0) { /* Line needed for resend was not cached */
-    rr_dev_log (dev, "; re-send request for unknown (too old) line %ld from cache size %d\n",
-		lineno, dev->sendsize[RR_PRIO_SENTCACHE]);
-    rr_dev_emit_error (dev, RR_E_UNCACHED_RESEND, reply, nbytes);
+  if (resent == 0) {
+    /* Perhaps line is in the resend queue, and we got an:
+     *     rs: 3
+     *     rs: 6
+     * type sequence so try peel forward the resend queue.
+     */
+
+    while (1) {
+      if (!(node = rr_dev_pop_from_queue (dev, RR_PRIO_RESEND)))
+	break;
+      debug_log ((dev, "; pop resend node line %d '%s' (%d bytes)\n",
+		  (int)node->line, node->block, node->blocksize));
+      if (node->line < lineno) {
+	rr_dev_prepend_to_queue (dev, RR_PRIO_SENTCACHE, node);
+	resent++;
+      } else { /* put it back and give up */
+	rr_dev_prepend_to_queue (dev, RR_PRIO_RESEND, node);
+	break;
+      }
+    }
+
+    if (resent == 0) {
+      rr_dev_log (dev, "; re-send request for unknown (too old) line %ld from cache size %d\n",
+		  lineno, dev->sendsize[RR_PRIO_SENTCACHE]);
+      rr_dev_emit_error (dev, RR_E_UNCACHED_RESEND, reply, nbytes);
+    }
   }
 
   dev->send_next = 1;
@@ -349,6 +369,9 @@ void
 rr_dev_reset_lineno (rr_dev dev)
 {
   dev->lineno = 0;
+  /* we invalidate all these line numbers */
+  empty_queue (dev, RR_PRIO_RESEND);
+  empty_queue (dev, RR_PRIO_SENTCACHE);
   rr_dev_enqueue_internal (dev, RR_PRIO_HIGH, "M110", 4, -1);
   dev->init_send_count = dev->dev_cmdqueue_size - 1;
 }
diff --git a/libraries/libreprap/fived.c b/libraries/libreprap/fived.c
index 28bf125f..7656b3bf 100644
--- a/libraries/libreprap/fived.c
+++ b/libraries/libreprap/fived.c
@@ -57,23 +57,22 @@ fived_handle_reply (rr_dev dev, const char *reply, size_t nbytes)
     size_t n_start = strcspn (reply, "123456789");
     if (n_start) {
       long long lineno = strtoll (reply + n_start, NULL, 10);
-      /* check if lineno is in the range of sent lines*/
-      if (lineno < dev->lineno)
-        return rr_dev_resend (dev, lineno, reply, nbytes);
-      else {
-	if (dev->lineno <= 1) {
-	  /* oh dear - most likely we re-connected to a device that
-	     had problems mid-flow, now we need to re-send the
-	     line-number reset as if it was this line-no it is asking
-	     for a re-send of, or there will be no peace */
-	  rr_dev_log (dev, "; resetting confused firmware with synthetic resend of line %d\n",
-		      dev->lineno);
-	  rr_dev_enqueue_internal (dev, RR_PRIO_HIGH, "M110", 4, lineno);
-	  /* re-start the print */
-	  rr_dev_resend (dev, 0, "synthetic restart", 16);
-	}
+
+      if (dev->lineno <= 1) {
+	/*
+	 * oh dear - most likely we re-connected to a device that
+	 * had problems mid-flow, now we need to re-send the
+	 * line-number reset as if it was this line-no it is asking
+	 * for a re-send of, or there will be no peace
+	 */
+	rr_dev_log (dev, "; resetting confused firmware with synthetic resend of line %d\n",
+		    dev->lineno);
+	rr_dev_enqueue_internal (dev, RR_PRIO_HIGH, "M110", 4, lineno);
+	/* re-start the print */
+	rr_dev_resend (dev, 0, "synthetic restart", 16);
 	return rr_dev_emit_error (dev, RR_E_UNSENT_RESEND, reply, nbytes);
       }
+      return rr_dev_resend (dev, lineno, reply, nbytes);
     } else
       return rr_dev_emit_error (dev, RR_E_MALFORMED_RESEND_REQUEST, reply, nbytes);
 
diff --git a/src/model.cpp b/src/model.cpp
index 1b27cd71..edc955e0 100644
--- a/src/model.cpp
+++ b/src/model.cpp
@@ -742,7 +742,8 @@ bool Model::handle_dev_fd (Glib::IOCondition cond)
     if (result < 0)
       error ("Error reading from device!", strerror (errno));
   }
-  if (cond & Glib::IO_OUT) {
+  // try to avoid reading and writing at exactly the same time
+  else if (cond & Glib::IO_OUT) {
     result = rr_dev_handle_writable (m_device);
     if (result < 0)
       error ("Error writing to device!", strerror (errno));