To reproduce:
- Add RadMenu with some items to a blank form.
- Initialize the menu like this:
Me.RadMenu1.RightToLeft = System.Windows.Forms.RightToLeft.Yes
Me.RadMenu1.DropDownAnimationEnabled = True
Me.RadMenu1.DropDownAnimationFrames = 30
Me.RadMenu1.DropDownAnimationEasing = RadEasingType.OutElastic

- Show the item drop down manually :
Private Sub RadMenuItem_MouseHover(sender As Object, e As EventArgs)
    Dim item As RadMenuItem = TryCast(sender, RadMenuItem)
    If item IsNot Nothing Then
        item.DropDown.Show()
    End If
End Sub