Minecraft server stops when you kick someone?

I have a problem when I kick someone from the server the server stops. The console then hangs up (it doesn't say that it will be stopped) and everyone flies off the server and then I have to do a reboot. (There's no information in the console) Does anyone know whether this is due to a plug-in, a script or perhaps the server properties?

There's certainly some plugin to blame.

Yes, I actually thought that too, but do you happen to know one of them?

No, if I host Minecraft, it will be vanilla…