When posting a form with xhrPost, dojo strips away all buttons values, and this is a documented design choice. My application needs the value of the clicked button to be sent along the rest of the form, so I worked around dojo by adding the value to the content dictionary you can pass to xhrPost: it works fine because dojo strips the button values before merging it with the content dictionary.

Trying to do the same thing with doio.io.iframe.send I discovered that the button value removal is done after the merge with the content dictionary. To get it work I had to create an hidden form field instead of the dictionary.

Is this a design choice or a bug? I think dojo.io.iframe.send should be changed to work like xhrPost.