Shifting reads and unreads marks on group pages -> chapter tab doesn't really work as intended.
If it's initially unread, shifting to read the first time works, but subsequent clicks try to mark it has read again, returning a 500 http code.
If it's initially read, shifting to unread the first time also works and subsequent clicks try to mark it has unread again, however, in this case, it returns a 200 http code.
If it's initially unread, shifting to read the first time works, but subsequent clicks try to mark it has read again, returning a 500 http code.
If it's initially read, shifting to unread the first time also works and subsequent clicks try to mark it has unread again, however, in this case, it returns a 200 http code.
