How to: Make Sure That a GridSplitter Is Visible
The Children of a Grid control are rendered in the order that they are defined in markup or code. GridSplitter controls can be hidden by other controls if you do not define them as the last elements in the Children collection or if you give other controls a higher ZIndexProperty.
To prevent hidden GridSplitter controls, do one of the following.
Set the ZIndexProperty on the GridSplitter to be higher than a control that would otherwise hide it. The following example gives the GridSplitter control a higher ZIndexProperty than the Button control.