Local table editor does not support joined tables

I noticed that when you have a complex data source, you cannot reliably use local table editing.

Repro: http://live.datatables.net/mayocawi/1/edit?js,console,output

1. Select a row
2. Click the edit button
3. Change the location
4. (Compare old value against new value in the table and console output)

Expected behavior
when changing the Location of a user, both the users.site and sites.name fields of a row are set to the selected value.

Actual behavior
only the users.site value is set to the selected value.

Example
"Pre-submit: site id = 2"
"Pre-submit: site name = London"
"Post-submit: site id = 3"
"Post-submit: site name = London"