wpf ViewBox - when scaling a DataGrid, the Grid lines are missing

I have a WPF Toolkit DataGrid control, contained within a Grid, i开发者_如何转开发nside a ViewBox control. The DataGrid has its own style with Black background, White Text and White Grid lines.

Some of the grid lines are missing from the grid (literally) from display, typically when there are 10 rows or more in the DataGrid. When I remove the ViewBox, it works fine (but I need scaling hence the use of the ViewBox).

I have not set many properties of the viewbox:

<Viewbox Stretch="Uniform" StretchDirection="Both">

Do I need to set other properties in order for the DataGrid to be scaled properly? Or because the DataGrid has its own customized style?

Thanks very much

Joe

Increased the Border size of the DataGridCells in the DataGrid Customized style.