User blog comment:Undead.exe/Breakpoint 0, Typography 0/@comment-86.218.28.29-20150520090909/@comment-303594-20150520144933

This is because I added an Abuse Filter to block this. It would have a nicer message, but unfortunately Abuse Filter doesn't work well with the new editor. IP users can't have custom JS/CSS pages. This would be a security risk as someone could create a page that affected all future users of that IP.

Before the filter, IPs could create these pages, they simply have no effect.