.net - Make Mouse Tilt Horizontal Scrolling Always Repeat?

I'm designing a form with a horizontal scroll bar docked at the bottom. I wanted to add support for side-scrolling using mouse tilt buttons and found this solution which, after a bit of tinkering, seemed to do the trick - that is, while the form only had GDI graphics drawn on its surface.

However, since then I've added some controls to the form and found that when the mouse is over any of them the tilt operation only fires once-at-a-time instead of repeatedly as it does when the mouse is over any other part of the form.To see what I mean (if you have a mouse with tilt buttons) dock a horizontal scrollbar onto the bottom of a form, add a few other controls and paste in this code:

Public Class Form1
Const WM_MOUSEHWHEEL As Integer = &H20E
Protected Overrides Sub WndProc(ByRef m As Message)

[code]....

You'll see that side-scrolling repeats when the mouse is over a blank part of the form, but only "one-shots" when it's over a control.I'm guessing the solution lies somewhere in the message's .Result value, but I'm at a loss as to what that should be. In fact I'm not even sure I'm returning a correct value anyway because the code in the original solution threw an exception to the DirectCast function so I swapped that for CType, which seemed to work okay. I've tried working it out using Spy++ but I can't see anything obvious.

UPDATE:I've noticed when I include 'Child' windows in Spy++ there are two (0x020E) messages and two return values, 1 then 0. I presume the message is being passed onto the control by the form. So I guess the question now is: can the message be prevented from being passed to the control? Or can the control's return value be intercepted and converted to 1?