Maybe bug?: REST + joined tables = blank joined column

I have a table with "equipment" column from a join (using check boxes in the UI) and "editor" using REST.

Joined columns are blanked (except for commas) on any edit submission.
Old value: CIETN01X, CIETN03X, CIVAR11X, CIVAR62X
New value: ,,,

If I re-edit the row, appropriate values of "equipment" are still checked, but they are never again displayed until I refresh the web page.

My return JSON from an edit follows:

{"id":"1","error":"","fieldErrors":[],"data":[],"aaData":null,"row":null,"children":null}

(If children and row are completely omitted, the same thing happens)

Further information about the table setup is in this post:
http://datatables.net/forums/discussion/12195/read-only-columns-displayed-only-in-datatable#Item_5