I've the same problem but on a Treeview control. When I have more than 8 items, Drag&drop crash on the "CumulativeValue" method in IndexTree class.
I think that this problem due to the constructor of IndexTree class :
.count = capacity;
.size = 8;
.size < capacity)
.size << 1;
.size << 1];
.itemDefaultValue = defaultValue;
When you drag an element, i think this element is temporary duplicated. So "size" property is smallest
is there a trick to solve this problem ?