Very easy to recreate.
Hover the mouse over the form, and without moving the mouse at all simply click the mouse button and you will notice the counter increase when you release the button.
Does anyone know why it fires the event? I also have noticed that some controls not only fire the event when the mouse button is released, but also when its pressed. So it fires twice for each mouse click.
Surely this is not by design. Microsoft describes this event as "Occurs when the mouse pointer is moved over the control."
There is no mention of it occuring when the user clicks a button.
Private cnt As Integer
Private Sub Form1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove
cnt = cnt + 1
Me.Text = "MouseMove: " & cnt