Create a ComboBox populated with some items. Select an item in the middle of the list (e.g. 10th). Now programmatically delete an item which is higher in the list than selected item (e.g. 2nd). The ComboBox selection will change. It will now display item which is two places before previous item (8th in this case). If you delete an item which is lower in the list than selected item, everything is OK.

Similar issue appears if you insert a new item before the selected item (selection now skips two places ahead).

I don't think ComboBox value should change when list is changed, unless currently selected item is deleted.