Hello,
A delete button should show up on each list item if the ICollectionItemPropertyDescriptor created for the related item has its CanRemove property returning true. You can see this in our "Collection New Items" QuickStart.
Our default ListItemPropertyDescriptor used for IList collections returns this for the CanRemove property:
return (!isCollectionReadOnly) && (list != null) && (!list.IsReadOnly) && (!list.IsFixedSize);
Are you sure your collection implements the basic IList interface and doesn't have IsReadOnly or IsFixedSize set?