Pixelmon 5.0.0 Beta9 problem

hey guys, been running the newest Pixelmon on my server and came across a problem.
Whenever two players use the trading station, an error comes up on the console and those players can’t use any of their pokemon after that until the server is restarted.
This is the error that comes up:

[16:26:55] [Server thread/FATAL]: Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException
	at java.util.concurrent.FutureTask.report(FutureTask.java:122) ~[?:1.8.0_91]
	at java.util.concurrent.FutureTask.get(FutureTask.java:192) ~[?:1.8.0_91]
	at net.minecraft.util.Util.func_181617_a(SourceFile:46) [h.class:?]
	at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:668) [MinecraftServer.class:?]
	at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:387) [ld.class:?]
	at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:613) [MinecraftServer.class:?]
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:471) [MinecraftServer.class:?]
	at java.lang.Thread.run(Thread.java:745) [?:1.8.0_91]
Caused by: java.lang.NullPointerException
	at org.spongepowered.common.event.tracking.phase.util.PacketPhaseUtil.handlePlayerSlotRestore(PacketPhaseUtil.java:101) ~[PacketPhaseUtil.class:1.10.2-2092-5.0.0-BETA-1746]
	at net.minecraft.network.NetHandlerPlayServer.redirect$onProcessRightClickBlock$0(NetHandlerPlayServer.java:551) ~[me.class:?]
	at net.minecraft.network.NetHandlerPlayServer.func_184337_a(NetHandlerPlayServer.java:679) ~[me.class:?]
	at net.minecraft.network.play.client.CPacketPlayerTryUseItemOnBlock.func_148833_a(SourceFile:55) ~[jj.class:?]
	at net.minecraft.network.play.client.CPacketPlayerTryUseItemOnBlock.func_148833_a(SourceFile:11) ~[jj.class:?]
	at org.spongepowered.common.network.PacketUtil.onProcessPacket(PacketUtil.java:121) ~[PacketUtil.class:1.10.2-2092-5.0.0-BETA-1746]
	at net.minecraft.network.PacketThreadUtil$1.redirect$onProcessPacket$0(SourceFile:39) ~[fl$1.class:?]
	at net.minecraft.network.PacketThreadUtil$1.run(SourceFile:13) ~[fl$1.class:?]
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) ~[?:1.8.0_91]
	at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_91]
	at net.minecraft.util.Util.func_181617_a(SourceFile:45) ~[h.class:?]
	... 5 more

Does it happen in the same way as this:

Does this happen every time that the trading station is used?

No, it doesn’t matter. Players have reported being unable to send them out after flying, or evolving or literally standing AFK.