Fix for taking a snapshot of a node running an image alias.

apt/manage_instance.in

@@ -902,11 +902,14 @@ sub DoImageTrackerStuff($$$$$$)
 	}
     }
     #
-    # System Image? We use the URN we get back from CreateSliver().
+    # System Image? We use the URN we get back from CreateImage().
     # The cluster will be the origin for the new image.
     #
     return 0
-	if ($blob->{'issystem'});
+	if (exists($blob->{'issystem'}) && $blob->{'issystem'});
+    # Image aliases are also considered system images.
+    return 0
+	if (exists($blob->{'isimagealias'}) && $blob->{'isimagealias'});
 
     my $image_urn     = $blob->{'urn'};
     my $copyback_uuid = $blob->{'version_uuid'};