We're using one version back from the latest telerik release and the grid setup is pretty straight-forward.
There is one detail grid for each row and each column on both the master and detail grids are template columns who have their values displayed with calls to Eval().
If InsertItemDisplay="top" everything looks fine, however InsertItemDisplay="bottom" causes the grid to render as in the attached screenshots.
Notice in the second screenshot the insert row looks fine on the detail grid which makes me think it's an issue with the expand indicator column on the master grid.
Can anyone else reproduce this?