The bug was declined as the feature service was "designed" this way. However, this "design" doesn't fall in line with the new editing environment in ArcGIS 10. The Editing Environment in ArcGIS 10 allows for multiple field symbolization and encourages it using templates.
I just ran into this problem when trying to create a feature service for use with ArcGIS Online and Collector. I want to symbolize the inventory Status of point features, but also need to show which points belong to which inventory Team. Showing Team assignment areas as polygons was my first idea, but the polygons render slowly in Collector. Having the ability to symbolize my point feature service on two attribute fields (Status, Team #) would have solved this problem nicely.
