Index: Globals.cpp
===================================================================
--- Globals.cpp	(revision 18395)
+++ Globals.cpp	(working copy)
@@ -647,23 +647,32 @@
 }
 
 
+static short RoundMouseWheelToWholeStep(int value)
+{
+	if(value > 0)
+		return mpt::saturate_cast<short>(mpt::align_up(value, WHEEL_DELTA));
+	else
+		return mpt::saturate_cast<short>(-mpt::align_up(-value, WHEEL_DELTA));
+}
+
+
 BOOL CModScrollView::OnMouseWheel(UINT fFlags, short zDelta, CPoint point)
 {
 	// we don't handle anything but scrolling just now
-	if (fFlags & (MK_SHIFT | MK_CONTROL)) return FALSE;
+	if(fFlags & (MK_SHIFT | MK_CONTROL))
+		return FALSE;
 
-	//if the parent is a splitter, it will handle the message
-	//if (GetParentSplitter(this, TRUE)) return FALSE;
-
 	// we can't get out of it--perform the scroll ourselves
-	return DoMouseWheel(fFlags, zDelta, point);
+	return DoMouseWheel(fFlags, RoundMouseWheelToWholeStep(zDelta), point);
 }
 
 
 void CModScrollView::OnMouseHWheel(UINT fFlags, short zDelta, CPoint point)
 {
+	zDelta = RoundMouseWheelToWholeStep(zDelta);
+
 	// we don't handle anything but scrolling just now
-	if (fFlags & (MK_SHIFT | MK_CONTROL))
+	if(fFlags & (MK_SHIFT | MK_CONTROL))
 	{
 		CScrollView::OnMouseHWheel(fFlags, zDelta, point);
 		return;