Block tag disappearing off the face of the earth

So, I used to have PBT as a block tag. One day, I check my watched list, see an image I dislike, and add PBT.  
It doesn’t work.  
I check the image. This is the only image for PBT ever. I check my content settings, and it’s not there either! I go to an image I know I blocked, and PBT isn’t there. I check the tag changes to see who removed it. Nobody removed it.  
Have I gone mad? What the heck happened?

Another one (image is NSFW, but this only links to tag changes)

I’d imagine that people remove it because it’s inherently unfair. Imagine if everyone got to put their own little tag on images that they didn’t like. There’d be dozens of tags on every image that had nothing to do with the art.

Well how should I keep it off in the mean time? And why are there no tag changes for the first time it disappeared?

Well for now you deal with it. And the first time was when the mods nuked it.

@soundtea  
Oh, ok. I mean, if it had showed up as being a mod in tag changes, I probably would have figured out pretty quick. :/

@Parzival  
filter the artist, meme name, character name, situation, sexual orientation, ETC tag instead.

I wiped it.
 
Tags are to describe and categorize images for the entire community, not for specific users. We have over 70k registered users (ie users that can use tag filters). Imagine if every one of them had one of these “block” tags.
 
Now imagine hell. They’re pretty similar.