Checkbox list DefaultValue only takes first value instead of all checked ones

I have a create-form with a checkbox list that takes PreValues from a checkbox list data type. When the form is submitted, a WorkFlow also saves the form as a node (many thanks to Tim and PublishFormAsPage)

Then I created an edit-form which takes DefaultValues not from the record, but from the currentNode, the node containing the edit-form. However, the checkbox list's DefaultValue only takes first value instead of all checked ones.

Is there a way to extend the existing checkbox list FieldType such that it parses multiple values?

Umbraco 4.7.1, Contour 1.1.2, custom workflows (PublishFormAsPage, UpdateFormAsPage) and custom FieldTypes (Label.cs from Contour.Contrib in App_Code folder)

Cheers,
León


This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/27498-checkbox-list-defaultvalue-only-takes-first-value-instead-of-all-checked-ones