I have recently upgraded to 4.6.19 which has solved issues to do with the updating of smart groups. However if I add a contact to a smart group it does not show the status of 'added' but shows the status to be 'smart'.
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