If you have the mouse above another control, the Windows Form will stop
receiving the MouseMove events, and the control which the mouse is above
will get those events. So if you want one event handler for the form and all
controls, you'd have to delegate the controls and forms MouseMove events to
the same event handler.

VB
AddHandler this.MouseMove, AddressOf(MyMouseMoveHandler)
AddHandler (this.Control1.MouseMove, AddressOf(MyMouseMoveHandler)

C#
this.MouseMove += new MouseEventHandler(MyMouseMovehandler)
this.Control1.MouseMove += new MouseEventHandler(MyMouseMovehandler)