=== modified file 'mixxx/src/controllers/midi/midicontroller.cpp'
--- mixxx/src/controllers/midi/midicontroller.cpp	2013-05-16 00:14:12 +0000
+++ mixxx/src/controllers/midi/midicontroller.cpp	2013-09-26 07:22:24 +0000
@@ -50,6 +50,13 @@
     // TODO(XXX): throw a hissy fit.
 }
 
+bool MidiController::isClockSignal(MidiKey &mappingKey) {
+    if ((mappingKey.key & MIDI_SYS_RT_MSG_MASK) == MIDI_SYS_RT_MSG_MASK) {
+        return true;
+    }
+    return false;
+}
+
 bool MidiController::matchPreset(const PresetInfo& preset) {
     // Product info mapping not implemented for MIDI devices yet
     Q_UNUSED(preset);
@@ -255,6 +262,12 @@
             target.first = control;
             target.second = options;
 
+            // Ignore all standard MIDI System Real-Time Messages because they 
+            // are continuously sent and prevent mapping of the pressed key.
+            if (isClockSignal(mappingKey)) {
+                return;
+            }
+
             // TODO: store these in a temporary hash to be applied on learning
             //  success, or thrown away on cancel.
             m_preset.mappings.insert(mappingKey.key,target);

=== modified file 'mixxx/src/controllers/midi/midicontroller.h'
--- mixxx/src/controllers/midi/midicontroller.h	2013-02-09 05:21:42 +0000
+++ mixxx/src/controllers/midi/midicontroller.h	2013-09-26 07:22:49 +0000
@@ -20,6 +20,9 @@
 #include "controllers/midi/midioutputhandler.h"
 #include "controllers/softtakeover.h"
 
+#define MIDI_SYS_RT_MSG_MASK 0xF8
+// from MIDI Message Table http://www.midi.org/techspecs/midimessages.php
+
 class MidiController : public Controller {
     Q_OBJECT
   public:
@@ -43,6 +46,8 @@
     virtual void visit(const MidiControllerPreset* preset);
     virtual void visit(const HidControllerPreset* preset);
 
+    bool isClockSignal(MidiKey &mappingKey);
+
     virtual bool isMappable() const {
         return m_preset.isMappable();
     }