Index: /trunk/src/VBox/Devices/Audio/DevHDA.cpp
===================================================================
--- /trunk/src/VBox/Devices/Audio/DevHDA.cpp	(revision 75421)
+++ /trunk/src/VBox/Devices/Audio/DevHDA.cpp	(revision 75422)
@@ -1979,7 +1979,8 @@
             switch (pCfg->DestSource.Source)
             {
-                case PDMAUDIORECSOURCE_LINE: enmMixerCtl = PDMAUDIOMIXERCTL_LINE_IN; break;
+                case PDMAUDIORECSOURCE_UNKNOWN: break;
+                case PDMAUDIORECSOURCE_LINE:    enmMixerCtl = PDMAUDIOMIXERCTL_LINE_IN; break;
 # ifdef VBOX_WITH_AUDIO_HDA_MIC_IN
-                case PDMAUDIORECSOURCE_MIC:  enmMixerCtl = PDMAUDIOMIXERCTL_MIC_IN;  break;
+                case PDMAUDIORECSOURCE_MIC:     enmMixerCtl = PDMAUDIOMIXERCTL_MIC_IN;  break;
 # endif
                 default:
@@ -1997,4 +1998,5 @@
             switch (pCfg->DestSource.Dest)
             {
+                case PDMAUDIOPLAYBACKDEST_UNKNOWN:    break;
                 case PDMAUDIOPLAYBACKDEST_FRONT:      enmMixerCtl = PDMAUDIOMIXERCTL_FRONT;      break;
 # ifdef VBOX_WITH_AUDIO_HDA_51_SURROUND
@@ -2014,6 +2016,9 @@
     }
 
-    if (RT_SUCCESS(rc))
+    if (   RT_SUCCESS(rc)
+        && enmMixerCtl != PDMAUDIOMIXERCTL_UNKNOWN)
+    {
         rc = hdaCodecRemoveStream(pThis->pCodec, enmMixerCtl);
+    }
 
     LogFlowFuncLeaveRC(rc);