Microsoft will not be issuing a hotfix for this issue. The issue is planned to be resolved in future versions of the product.
In order to support this scenario, the staging table must have a unique index. First step is to create a customization that introduces a unique index.
- Open the SalesOrderHeaderStaging table in the designer in Visual Studio
- On the StagingIdx:
- Set the "Allow Duplicates" property to "No"
- Set the "Alternate Key" property to "Yes"