What is Dockable property set to?

>For multiple times I have created a splash screen. This one gives me trouble: the titlebar is showing, without any objects, but still. Most of the times the titlebar container is white, rarely it is dark grey
>The properties of this splash.scx are:
>autocentre = .t.
>backcolor = 255,255,255
>borderstyle = 1
>caption = (none)
>height = 540
>TitleBar = 0
>width = 568
>WindowType = 1
>
>setting the other objects in the title bar like Min- Max- Button to .F. makes no difference.
>
>Any clue how to solve?
>
>Regards,
>Koen