I have a column in an ultragrid set to GroupByMode.Date. The column has null and not null values. When I sort the column in descending order and group on the sorted column the null date values are getting grouped with the last not null value. If the column is not sorted, or sorted in ascending order, then the null values are not grouped with any not null value when the column is grouped on.

I'm not sure why changing the order is affecting the contents of each grouping?

I've attached a small project that demonstrates the problem.