Index: /trunk/src/VBox/Devices/Storage/DevBusLogic.cpp
===================================================================
--- /trunk/src/VBox/Devices/Storage/DevBusLogic.cpp	(revision 49577)
+++ /trunk/src/VBox/Devices/Storage/DevBusLogic.cpp	(revision 49578)
@@ -3934,5 +3934,10 @@
                                 N_("BusLogic configuration error: failed to read Bootable as boolean"));
     Log(("%s: fBootable=%RTbool\n", __FUNCTION__, fBootable));
-    rc = CFGMR3QueryStringDef(pCfg, "ISACompat", achISACompat, sizeof(achISACompat), "Alternate");
+
+    /* Only the first instance defaults to having the ISA compatibility ports enabled. */
+    if (iInstance == 0)
+        rc = CFGMR3QueryStringDef(pCfg, "ISACompat", achISACompat, sizeof(achISACompat), "Alternate");
+    else
+        rc = CFGMR3QueryStringDef(pCfg, "ISACompat", achISACompat, sizeof(achISACompat), "Disabled");
     if (RT_FAILURE(rc))
         return PDMDEV_SET_ERROR(pDevIns, rc,