I don't want to sound alarmist, but this has the potential to be a very big problem, and so far things are adding up.
A while back a support tech logged the following bug: #NIM087819 Feature service shows no editable layer error when the feature class was from workgroup sde (sqlexpress) with OS authentication . Looking back on it, that was a 2012 instance (Express).
So now getting SQL Server 2012 Standard up and running (Enterprise) I spent some time with both the SDE/Geodata team and Server Implementation. When editing a feature service with a SQL 2012 RDBMS in you in ArcGIS Desktop receive an error 'no editable workspace'. However, when editing via arcgis online, the feature service edits as expected. All permission/privileges have been verified as correct.
This got one of the techs thinking about this bug: NIM085096Uploading mobile edits to an SQL 2012 database fails with Mobile 3.0, 3.1, and 10.1.1
The correlation here being that both ArcGIS Desktop and Mobile access the data via SOAP, while the ArcGIS online was using the REST endpoint. I'm starting to think that 2 Bugs are indeed related. If there is indeed a bug preventing SOAP based edits and feature services are not going to work for Desktop...then this is a big issue.
Again, I'm quite ignorant to the means by which server/sde handles the editing transactions so I can only hope the above isn't implying what I think its implying (no fix). Even then, not being able to edit a feature service is a big deal.
I expect to hear a follow-up on this soon, and will post any additional info I receive.
