[MC-64691] Server Crash java.util.ConcurrentModificationException

My snapshot server crashed twice, since last update. Here is error:
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
at java.util.HashMap$KeyIterator.next(HashMap.java:828)
at qi.a(SourceFile:163)
at net.minecraft.server.MinecraftServer.y(SourceFile:614)
at pk.y(SourceFile:303)
at net.minecraft.server.MinecraftServer.x(SourceFile:530)
at net.minecraft.server.MinecraftServer.run(SourceFile:446)
at java.lang.Thread.run(Thread.java:662)

And crash reports in attachments

Environment

Minecraft Version: 14w31a
Operating System: Linux (i386) version 2.6.32-5-686-bigmem
Java Version: 1.6.0_26, Sun Microsystems Inc.
Java VM Version: Java HotSpot(TM) Client VM (mixed mode, sharing), Sun Microsystems Inc.
Memory: 149344448 bytes (142 MB) / 518979584 bytes (494 MB) up to 518979584 bytes (494 MB)
JVM Flags: 2 total; -Xmx512M -Xms512M
IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 98
Profiler Position: N/A (disabled)
Player Count: 1 / 8; [qr['CygnusAtratusUA'/437255, l='world', x=208.70, y=71.00, z=204.08]]
Is Modded: Unknown (can't tell)
Type: Dedicated Server (map_server.txt)