Smart Groups - Added contacts show status of 'smart' not 'added'
I just tested this in 4.5.5 and 4.7.9 (sorry, don't have a 4.6 test environment) and the status of a contact added to a smart group is indeed "added", so unless it is a bug with your specific version, perhaps the contact you believe to have added actually fit the criteria of the smart group to begin with? In any case, upgrading will resolve the issue.

Kind regards,
Tamar