Unbound Field Problems

Hi all :)

Consider the following:
I have orders from an order table, a table for delivered items (as customer might not get wat is ordered due to various reasons), a client table and an item table.

My current problem revolves around the packers form, to enter what is delivered in a simple manner. The main form shows a customer and the sub form shows the delivery form. This delivery form shows fields for one customer, and the rows are "per item":
- Item name
- sum Ordered
- packed (unbound)
- delivered (checkbox)
- actual delivered
- Diff (between "sum ordered" and "actual delivered")

My first limitation is that the order numbers are obtained by crosstabbing and various unions and joins, so the rows are not directly updatable. The workflow I vision is:
1. The "packed" field should have a default value of "sum ordered"
2. User verifies or changes the packed field to the number of items being packed
3. User then clicks the "delivered" checkbox and the system inserts a row in the delivered table, refreshes the forrm and the "actual delivered" should be filled in as well as the "delivered" checkbox checked
4. At some point user wants to change delivered item and updates the "packed" field and the system changes the "delivered" checkbox to unchecked)
5 user verifies change of number and checks the "delivered" checkbox and the system updates the delivered record and does a refresh

At first I tried to have the "packed" constrol source to "iif(isNull([actual_delivered]);[sum_ordered];[actual_delivered]". This expression works, but when I try to change the value is says "form is read-only" (when I try to change some other field it says "Th recordset is not updateable"). I then took away the expression and it was updateable, but as soon as the field is updated, all the rows gets the same value.

I thught about setting the "packed" value in an event, but it seems as long as it is unbound, all rows will have the same value (tried on curent). To me it feels like a chicken and egg situation, which usually means something is not done right. I also believe that I can "fake" the checking of the checkbox by using a "mouse down" or "key down" to catch the user's intention and then update the underlaying values and do a refresh. It doesn't feel right, but that's the direction this is taking because of the uneditableness.

Has anybody got an idea of how to mix non-updateable and updatable fields in the same subform and have seperate values in an unboud field? or a bettwe way of doing this?

Thaks :D