RadGridView problem using ExpandAllGroups

Hello,

I'm having trouble to automatically expand all groups within a RadGridView. I set the AutoExpandGroups to true and also call the RadGridView's method ExpandAllGroups(). It does expand all the groups, but it also adds an unwanted white space to my grid, that vanishes after I manually collapse one of the groups.

I also tried to set the GroupRenderMode to Flat. It solves the white space issue, but it adds unwanted information to my groups' headers.

Is there a way to make it work properly?

*Telerik UI for WPF version 2015.3.930.45

Thanks in advance.