There is a bug in sales direct invoice item drop-down list. After adding a line,when you shift focus to next and open the drop-down list and then decide to change the item you have just selected, it looses the drop-down list icon.

Also there is a bug in sales direct invoice when you use F4 key you are able to see items which you have marked as "exclude from Sales". From this window you can select and insert items which are marked as excluded from sales. These items should be filtered out in sales direct invoice F4 key function.