As per this update: http://issues.umbraco.org/issue/CON-1409

We have been playing around with this event (UmbracoFormsController_FormPrePopulate) and it works well for new forms.

However if we try to get data from an api in an answer type on one form section then move to the next.

The event is triggered and the values are set however they don't appear in the form fields.

So with this:

        if (nameField != null)
    {
        //Set the value to be pre-filled as 'Greg'
        nameField.Values = new List<object>() { "Greg" };
    } // putting breakpoint here the value is Greg

However when viewing the forms once rendered the value isn't shown.

Has anyone used this event mid form?