diff --git a/doomsday/engine/portable/include/window.h b/doomsday/engine/portable/include/window.h
index 48158a6ae7..cc262cd905 100644
--- a/doomsday/engine/portable/include/window.h
+++ b/doomsday/engine/portable/include/window.h
@@ -291,12 +291,18 @@ void Window_RestoreState(Window* wnd);
 /**
  * Activates or deactivates the window mouse trap. When trapped, the mouse cursor is
  * not visible and all mouse motions are interpreted as deltas.
+ *
+ * @param wnd     Window instance.
+ * @param enable  @c true, if the mouse is to be trapped in the window.
+ *
+ * @note This is a C wrapper for Canvas::trapMouse().
  */
 void Window_TrapMouse(const Window* wnd, boolean enable);
 
 void* Window_NativeHandle(const Window* wnd);
 
 #ifdef _DEBUG
+/// @todo Get rid of this; libdeng2 should do debug output.
 void debugPrint(const char* msg);
 #endif
 
diff --git a/doomsday/engine/portable/src/canvas.cpp b/doomsday/engine/portable/src/canvas.cpp
index c6df87e807..b3a6fecaee 100644
--- a/doomsday/engine/portable/src/canvas.cpp
+++ b/doomsday/engine/portable/src/canvas.cpp
@@ -70,25 +70,33 @@ struct Canvas::Instance
     {
         if(mouseGrabbed) return;
 
+        // Tell the mouse driver that the mouse is supposed to be trapped now.
         mouseGrabbed = true;
+        Mouse_Trap(true);
 
-        // Start grabbing the mouse now.
+#ifndef WIN32
+        // Start tracking the mouse now.
         QCursor::setPos(self->mapToGlobal(self->rect().center()));
         self->grabMouse();
         self->setCursor(QCursor(Qt::BlankCursor));
         qApp->setOverrideCursor(QCursor(Qt::BlankCursor));
-
         QTimer::singleShot(1, self, SLOT(trackMousePosition()));
+#endif
     }
 
     void ungrabMouse()
     {
         if(!mouseGrabbed) return;
 
-        mouseGrabbed = false;
+#ifndef WIN32
         self->releaseMouse();
         qApp->restoreOverrideCursor();
         self->setCursor(QCursor(Qt::ArrowCursor)); // Default cursor.
+#endif
+
+        // Tell the mouse driver that the mouse is untrapepd.
+        mouseGrabbed = false;
+        Mouse_Trap(false);
     }
 };
 
@@ -339,7 +347,7 @@ void Canvas::mouseReleaseEvent(QMouseEvent* ev)
     if(!d->mouseGrabbed)
     {
         // Start grabbing after a click.
-        Mouse_Trap(true);
+        trapMouse();
         return;
     }
 
diff --git a/doomsday/engine/portable/src/mouse_qt.c b/doomsday/engine/portable/src/mouse_qt.c
index fef50e23fc..78290828e1 100644
--- a/doomsday/engine/portable/src/mouse_qt.c
+++ b/doomsday/engine/portable/src/mouse_qt.c
@@ -21,6 +21,7 @@
  * 02110-1301 USA</small>
  */
 
+#include "dd_share.h"
 #include "sys_input.h"
 #include "window.h"
 #include <string.h>
@@ -75,7 +76,8 @@ static void Mouse_Qt_GetState(mousestate_t *state)
 
 static void Mouse_Qt_Trap(boolean enabled)
 {
-    Window_TrapMouse(Window_Main(), enabled);
+    // nothing to do -- the window will submit input to us when trapped
+    DENG_UNUSED(enabled);
 }
 
 void Mouse_Qt_SubmitButton(int button, boolean isDown)
diff --git a/doomsday/engine/portable/src/window.cpp b/doomsday/engine/portable/src/window.cpp
index bcf7f07329..443621edae 100644
--- a/doomsday/engine/portable/src/window.cpp
+++ b/doomsday/engine/portable/src/window.cpp
@@ -184,7 +184,7 @@ struct ddwindow_s
             {
                 if(DisplayMode_Change(mode, true /* fullscreen: capture */))
                 {
-                    Mouse_Trap(true);
+                    Window_TrapMouse(this, true);
 
                     geometry.size.width = DisplayMode_Current()->width;
                     geometry.size.height = DisplayMode_Current()->height;
@@ -899,7 +899,7 @@ static void windowFocusChanged(Canvas& canvas, bool focus)
     {
         DD_ClearEvents();
         I_ResetAllDevices();
-        Mouse_Trap(false);
+        Window_TrapMouse(wnd, false);
     }
 
 #if 0