Update node with services doesn't work for text_list widget
Maybe how you are updating the node i.e node_save() , The $node object that needs to be passed might not have the correct structure for the select list, 

$node-&gt;body[LANGUAGE_NONE][0]['format'] = 'something'; 


You can always try to node_load($nid) and watchdog it to see the structure of your select field, and then verify if you are creating the $node object correctly before doing node_save().

This is just my guess, I can provide more correct answer once I can see the relevant code.

Cheers