As designed If you tag a user when editing a post the user does not get an alert.

[wdb]

I'm not certain if this is a feature or a bug but it appears that if you edit a post and add a user tag that tag does not get processed and the user does not get an alert.

 

[Mike Edge]

Correct, they only receive the alert if included in the post, editing does not trigger it.

 

[Jeremy]

Its as designed. There is no reliable way to track whether user X was alerted for the post previously or if the tag for User X is new. This works identical to how quotes alert if you edit them in.

 

[Amaury]

I did make a suggestion on this behavior if anyone's interested.