does the actual version of the xamDataGrid supports row details? The last post I found was http://community.infragistics.com/forums/p/43348/238054.aspx#238054. Does this sample work when colums (fields) can be added by a User using the FieldChooser?
It has been a while since you have made your post, in case you still need support I will be glad to assist you further. I suppose the other community members can benefit from this answer as well. I have been looking through your post and the one that you have linked. I tested the sample that Alex has been provided and add a FieldChooser and everything works normal and as expected.
Feel free to write me if you have further questions.