radio_button simple array doesn't work

[johrstrom]

Consider the form below. Both of these have select options that are defined as an array of scalars (an array of strings).

However, only one works (the select widget leftright).

form:
  - updown
  - leftright
attributes:
  updown:
    widget: 'radio_button'
    options:
      - up 
      - down
  leftright:
    widget: 'select'
    options:
      - left
      - right

The radio_button fails with this error complaining about the fact that we're trying to access the second field of the array for the label.