Somehow everytime I update my blacklist it just revert to my old blacklist after i clicked save setting. why is that?

I'm guessing something about your browser is refusing to accept changes to cookies or something.

Everyone usually suggests clearing your cookies and restarting your browser. So you might start with that and see what happens.

Next up would be to try another browser completely.

well, I'm kind of person who cleared up all cookies once in two weeks, but still no avail
trying another browser? done that too. Heck I even try on another computer but still no avail.
Using chrome by the way

While trying to duplicate your problem I used a tag I don't care about: "Woody"

For some reason, blacklisting it only actually blocked 2 out of the 10 images that came up. Unless it needs more time or something.

After removing the tag from the blacklist, those 2 images are currently still blocked.... unless it needs more time or something.

But the tag no longer appears on the list. If it is really is a problem for multiple computers, it could be Gelbooru's end. Or your IP.