Why does Button.DoubleClick not fire in WinForms when MouseUp opens another form?

[IT_Researcher]

In a VB.NET Winforms application, we have a button.
On button click i.e. Button1.MouseUp event, it opens another form.
But when we double click on the button, the double click splits into two single clicks i.e. first single click opens another form (Button1.MouseUp event) and second single click happens on the now opened form which shows a message (MyBase.MouseUp event).

Public Class Form1
    Private Sub Button1_MouseUp(sender As Object, e As EventArgs) Handles Button1.MouseUp
        Dim form = New Form1
        form.ShowDialog()
        form.Dispose()
    End Sub

    Private Sub Button1_DClick(sender As Object, e As EventArgs) Handles Button1.DoubleClick
        MsgBox("double click")
    End Sub

    Private Sub Form1_MouseUp(sender As Object, e As MouseEventArgs) Handles MyBase.MouseUp
        MsgBox("Mouse Up")
    End Sub
End Class

Why does this unexpected behaviour happen and how to handle this?
Why isn't the Button1.DoubleClick event called on double clicking the button?

We tried giving sleep() before form.ShowDialog() but it made no difference. We also tried using PeekMessage in the child form's Load event to discard pending click messages from the message queue, but we are looking for alternative, cleaner methods.