Error on save checkbox, radio and dropdown values

[Jorgenh]

When adding a value and saving it the error as shown above in the attachment occurs. The error log shows the following lines:

INSERT INTO `modx_formalicious_answers` (`field_id`, `name`, `rank`, `published`, `selected`, `subfield_id`) VALUES (368, 'test', 1, 1, 0, 0)
Array
(
    [0] => 22007
    [1] => 1366
    [2] => Incorrect integer value: '' for column `xxxxx`.`modx_formalicious_answers`.`subfield_id` at row 1
)

It seems that somehow the value of '0' gets replaced by an empty string.
Altering the default value doesn't make a difference.