Today I deleted a post of mine with 3 points and undeleted it later. There is this badge called Disciplined (Delete own post with score of 3 or higher), it was awarded and it remained even after undeleting it.
I guess this is a bug or am I wrong and this is an expected behavior?
As far as I can see, I am not supposed to own this badge anymore.
Regular badges will not be revoked except in very special circumstances.
Regular badges, however, once earned, are yours to keep. Even if the criteria by which you earned a badge have changed (the post was deleted, you got downvoted, etc.) you get to keep your badge. If you qualify for the same badge again (another post earns you a post-related badge, for example), you won't be penalized either (source).
Regular in this context is opposed to tag badges that come with privileges (e.g. a gold tag badge gives you the right to unilaterally close a question as a duplicate of another question with that tag).
