https://gist.github.com/kukelekuuk00/ade3b6a1485788fb1250

Here I have a piece of code that lets me hook into creating, interacting and destroying signs. Or at least, that's what it was supposed to do. I cut out most of the code. Right now only the creating and interacting part remains.

The problem I'm having here is that whenever I create signs I can't break them any more. They don't even call a blockbreakevent. But the moment I remove the sign type from the titles array it'll work just fine. I can't wrap my head around this. It makes no sense. By all means it SHOULD call the blockbreakevent, but it doesn't.

http://www.mediafire.com/download/b44budwrj09tlm9/SignAPITest-1.0-SNAPSHOT.jar

The jar file. I tested it on craftbukkit and spigot 1.9. (but it happens on previous versions, too)
You can reproduce the bug by creating a sign with "[Test]" on the top line, case sensitive. If it works it should turn blue. And then you can't break it any more. You can still break the block it's attached to, but the sign itself won't break. It doesn't even call the blockbreakevent.