Partial itemFulfilment still sets Sales Order to completely fulfilled

We need to mark sales orders partially fulfilled if not all items have shipped yet.

I've rewritten code to try creating itemFulfilment records many different ways and no matter what, the SO always ends up "completely" fulfilled.

I'm using c# with 2011.1 web services.

Things I've tried:

* Create new item fulfilment from scratch (without using initialize)

* Created new item fulfilment with initialize (to get reference to existing IF record)

* Add only line items that have been fulfilled

* Add all line items, explicitly setting quantityRemaining = quantity (where the item has not been fulfilled), and setting quantityRemaining = 0 for those fulfilled.

* Trying variations with ReplaceAll = true, and trying variations again with ReplaceAll = false.