Index: /trunk/src/VBox/Frontends/VirtualBox/src/runtime/fullscreen/UIMachineWindowFullscreen.cpp
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/runtime/fullscreen/UIMachineWindowFullscreen.cpp	(revision 61490)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/runtime/fullscreen/UIMachineWindowFullscreen.cpp	(revision 61491)
@@ -353,4 +353,15 @@
 
 #if   defined(VBOX_WS_WIN) || defined(VBOX_WS_X11)
+# if defined(VBOX_WS_WIN) && QT_VERSION >= 0x050000
+    /* On Windows you can't just resize/move Qt5 QWidget to required host-screen
+     * because for simple normal QWidget maximum possible window size is limited
+     * by the available geometry and Qt5 bumps it out to the main host-screen in
+     * such case, need to tell window it will be full-screen without showing it. */
+    setWindowState(Qt::WindowFullScreen);
+    /* If there is a mini-toolbar: */
+    if (m_pMiniToolBar)
+        m_pMiniToolBar->setWindowState(Qt::WindowFullScreen);
+# endif /* VBOX_WS_WIN && QT_VERSION >= 0x050000 */
+
     /* Set appropriate geometry for window: */
     resize(workingArea.size());