It should work, does it produce an incident and just not block or is there no incident or blocking? If there is neither an incident or block, then it's likely either your policy or agent configuration isn't properly configured to detect the event.
Try making your policy simply detect any 'Printer/Fax' event, with no user specified. If this produces the incident/blocks, then add the user (you don't specify domain name in the Sender Pattern lists, just the username) or target the user through User Groups / Directory Connections. Also try printing in a different program (Office is probably best choice) to make sure it's not a compatibility issue.
You can also pull logs via Agent Overview, then pull log from Endpoint Server and search for the timestamp you did the printing - it should show the event even if an incident wasn't raised. If there is no event, then make sure Printer/Fax channel is enabled in Agent Configuration and you don't have some file filters that are affecting the bypassing of the print action.
Dean