Index: /trunk/src/VBox/VMM/VMMAll/APICAll.cpp
===================================================================
--- /trunk/src/VBox/VMM/VMMAll/APICAll.cpp	(revision 61581)
+++ /trunk/src/VBox/VMM/VMMAll/APICAll.cpp	(revision 61582)
@@ -2319,5 +2319,5 @@
                     if (!fActive)
                     {
-                        ASMAtomicWriteBool(pfActiveLine, false);
+                        ASMAtomicCmpXchgBool(pfActiveLine, false, true);
                         break;
                     }