edit form with referencefield returns object with string

[xyzones]

I have my model definition including reference field. Form is saved correctly, however when editing the data the reference fields are not returned correctly.

# object.to_json() 
{
...
 'Builder': <Choices: Choices object>,`
...
}

# form.data 
{
...
'builder': 'Choices object',
...
}

I would expect to have the Choices object id returned not the object as a string.

What am I missing?

Regards,

Attila