I have looked our correspondence about your problem and it seems that there is no problems with the grid. There is a problem with your model. It returns the wrong type in EditRole. I will building your example again tomorrow and will let you know the results by email.
P.S. Regarding your request of the new features - disabling button in the cell.
This feature has been implemented and will be available in the release of the grid which is planned this week or early next.
In your example 'relationmode' there are two columns with comboboxes on
the page Relation Mode. When you double-click f. e. on the city 'Oslo'
then there is a cursor after the 'o' and you can edit 'Oslo'. When i
insert instead 'Oslo' the text 'Berlin' than 'Berlin' is add in the other
dropdownlist for that column. What i want is only the possibility to
select a city from the dropdownlist. I don't want to see a cursor after
the last character and don't want to edit the text.