Can I clear all values from a pick list in Campaign Monitor and sync to Salesforce?

You can set up field mappings from Campaign Monitor to Salesforce.  If you working with pick list values we will update Salesforce every time the sync runs successfully.  However, if you remove all pick list values in Campaign Monitor and run the sync it will not update the correspond Salesforce record.  

This is a known limitation with Campaign Monitor APIs.  When a pick list field is empty it is not include in the API call we make and therefore the sync has no knowledge of the change.

The work around is to include a none value (or similar) that a person could select so at least one value is included in the pick list.