ChrisM@Work (1/30/2014)

---

It's by design, Kapil. There are two steps to the update/insert - a read to determine the rows which will be affected (by the join to source) and then the update/insert. The read remains unchanged throughout as a static reference - in other words, a snapshot. The purpose of this is to ensure that changes occur in a predictable manner. It's called Halloween Protection and Craig Freedman describes it far better than I can here.

It's up to you to shape your source data appropriately.