ConcurrentModificationException Crash MinecraftServer 1.8.1

MinecraftServer 1.8.1 is crashing consistently for me. This is my kid's server and we have not installed any mods. There are a lot of log lines about setting player scores and then this exception. This exception happens even if no one is connected to the server.

java.util.ConcurrentModificationException
at java.util.TreeMap$PrivateEntryIterator.nextEntry(TreeMap.java:1100)
at java.util.TreeMap$KeyIterator.next(TreeMap.java:1154)
at qu.a(SourceFile:574)
at qu.a(SourceFile:554)
at bfw.a(SourceFile:259)
at bfw.a(SourceFile:114)
at qt.b(SourceFile:160)
at qt.a(SourceFile:204)
at qu.a(SourceFile:766)
at net.minecraft.server.MinecraftServer.a(SourceFile:361)
at net.minecraft.server.MinecraftServer.s(SourceFile:384)
at pf.run(SourceFile:716)