downtime.start being overwritten

We are trying to auto open incidents in Service Manage by using web services to pass in information from Scorch.

The incidents create fine.  The issue is that we pass in the date/time for the Outage Start Time from Scorch (downtime.start) but Service Manager is overwriting that value we pass in with the ticket creation date.  I have gone into the Incident workflow and removed the rulesets im.standard.set.default.values and im.asgnchg.init but that doesn't help.

Any ideas when and where this value is being written to the Inicdent?