Provide "intelligent" record navigation when if cell activation is disabled
In your sample application (for example XamDataGrid -> Style -> Row Summary Styling) if you group the grid and press "down" on the last data record of a group, the grid will skip the summary record, expand the following group and select the first data record of that group.
This reasonable behaviour is deactivated when cell activation disabled (ie. only record selection is possible).
In regard to summary records in particular, I believe the XamDataGrid does not behave correctly. When you press "down" on the row before a summary record, the dotted focus border will not disappear, it is not apparent to the user that the focus has changed (and thus also not apparent that pressing down again will go to the next row).
The group rows behave correctly in this regard, because when if they do not expand, they get the focus border.