ISB UOM Tracking for External Sourced Items

Hello all,

I don't often support ISB in my organization, so I apologize up front if this is an elementary question.  I've been unable to find the answer on MOS or in the user/implementation guides.

We have an item set up with a primary UOM of "feet".  We have the tracking UOM set to "primary".  This is true in both our item master and the transaction organization.

Now, the item is placed on a sales order in OM with the source as "external", and the quantity on the line in OM is 800.  The external PO is opened with one line for qty 800 and the receipt is done for one line, qty 800.  The order line closes in OM.