Checkboxes are filtered, but parameter isn't correctly set

Hello,
The bug I encounter:

• with OG and formfilter
• filter "Groups" fieldset
• create an node inside a group (by passing group id inside URL)
• edit this node
• when you submit the node modification:
• you get a PHP error (invalid argument passed to foreach), because $node->og_groups is not an array anymore, but a simple value
• the node isn't in the group anymore

When I don't filter "Groups" fieldset, there is no problem. No problem, also, when the node is not created inside a group.
Maybe formfilter doesn't handle checkboxes and array parameters well ?

Thank you for your feedback,
David