Modify Node Field action creates redundant entries in field table

Steps to recreate:

1. Install Drupal
2. Install CCK
   • Content
   • Option Widgets
   • Text
3. Enable Views
4. Enable VBO
5. Create field (Text -> Checkboxes/Radio Buttons)
   • Field name -> 'test'
   • Number of values -> Unlimited
   • Allowed values list -> Two unique values
     • value1|Value1
     • value2|Value2
6. Create Action -> Modify Node Fields
   • Select the CCK text->checkboxes/Radio buttons created earlier
   • Select the "Add" Column
   • Select both CCK checkboxes
7. Create a View (type->node)
   • Style -> Bulk Operations
   • Under "Selected Operations" select the action you created earlier
   • Create a page display for the view, give at URL, add at least one field
8. Create a node
9. Navigate to the VBO, select the node you created and execute the VBO at least twice

At this point we have exactly one node and both of the example checkboxes should be checked.

Expected result:
Database table {content_field_test} has 2 rows in it

Observed result:
Database table {content_field_test} has 4 rows in it - two for each time the VBO was executed.

VBO will continue to add values for the checkboxes each time the VBO is run. If you edit and save the node, the extra values are deleted from the table.

I suspect this stems from the fact that you need to select "Unlimited" for the number of values on a CCK checkbox/radio button field in order to display checkboxes (instead of radio buttons). But a single node should never have multiple values for a single checkbox.

My workaround is to run a query that deletes all "duplicate" rows (except for the one with the lowest delta) each time the VBO is executed.