Minecraft server hangs mid-startup

Our snapshot server won't start up properly. This started happening this week, the server was running fine on 14w11b before. This is what happens when I try to start the server:

$ java -jar minecraft_server.jar nogui
[17:42:03] [Server thread/INFO]: Starting minecraft server version 14w11b
[17:42:03] [Server thread/INFO]: Loading properties
[17:42:03] [Server thread/INFO]: Default game type: SURVIVAL
[17:42:03] [Server thread/INFO]: Generating keypair
[17:42:03] [Server thread/INFO]: Starting Minecraft server on *:25565

After the last line it just sits there doing nothing. It also uses an unusually low amount of memory. In the Minecraft server list the server shows up with “Old” as the version.