I was building in my world and a zombie happened to past in between the iron bars I was placing and it made this unique error I found, I don't exactly know what to call this bug but I did some looking around and no one has found it yet from what I saw. The video will probably explain more... I'm not the best writer...

https://youtu.be/J82NmdJ1WRc

I've done a little bit more testing and I've found it also happens with glass panes, stairs of any kind, walls/fences of any kind... heres an image to better show it

https://i.imgur.com/yAyqizC.png