I have Crumbly Writer's story The Cuckoo's Progeny in my library.
He completed the story on chapter 27. After I read the original chapter 27, it dropped off my active serials list as expected.
Then he removed chapter 27 and added a cast list in it's place.
Now the story is back in my active serial list, it's not dropping off and the yellow highlight in the update notes column indicating new unread chapters isn't going away, despite the fact that I have read the cast list.