Not able to connect to dedicated server anymore with v0.8.1

[Pilzinsel64]

No Thermos is used, just Forge with lwjgl3ify. Issue happens since v0.8.1. The last working version is v0.8.0. Took me two hours to find this out.

[07:42:34] [Netty Client IO #2/ERROR] [FML]: NetworkDispatcher exception
io.netty.handler.codec.DecoderException: java.lang.IndexOutOfBoundsException: readerIndex(8) + length(225935) exceeds writerIndex(85415): UnpooledHeapByteBuf(ridx: 8, widx: 85415, cap: 85415)
	at Launch//io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:263) ~[netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:131) ~[netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:337) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:323) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:173) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:337) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:323) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.handler.timeout.ReadTimeoutHandler.channelRead(ReadTimeoutHandler.java:149) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelHandlerContext.invokeChannelRead(DefaultChannelHandlerContext.java:337) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelHandlerContext.fireChannelRead(DefaultChannelHandlerContext.java:323) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:785) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:100) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:480) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:447) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:341) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101) [netty-all-4.0.10.Final.jar:?]
	at java.base/java.lang.Thread.run(Unknown Source) [?:?]
Caused by: java.lang.IndexOutOfBoundsException: readerIndex(8) + length(225935) exceeds writerIndex(85415): UnpooledHeapByteBuf(ridx: 8, widx: 85415, cap: 85415)
	at Launch//io.netty.buffer.AbstractByteBuf.checkReadableBytes(AbstractByteBuf.java:1160) ~[netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.buffer.AbstractByteBuf.readBytes(AbstractByteBuf.java:668) ~[netty-all-4.0.10.Final.jar:?]
	at Launch//net.minecraft.network.PacketBuffer.readBytes(SourceFile:586) ~[et.class:?]
	at Launch//net.minecraft.network.play.server.S26PacketMapChunkBulk.func_148837_a(S26PacketMapChunkBulk.java:106) ~[gz.class:?]
	at Launch//net.minecraft.util.MessageDeserializer.decode(SourceFile:40) ~[ez.class:?]
	at Launch//io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:232) ~[netty-all-4.0.10.Final.jar:?]
	... 16 more

[07:42:34] [Netty Client IO #2/ERROR] [FML]: NetworkDispatcher exception
io.netty.handler.codec.DecoderException: java.io.IOException: Packet was larger than I expected, found 85390 bytes extra whilst reading packet 3
	at Launch//io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:263) ~[netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:196) ~[netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelHandlerContext.invokeChannelInactive(DefaultChannelHandlerContext.java:237) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelHandlerContext.fireChannelInactive(DefaultChannelHandlerContext.java:223) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:214) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelHandlerContext.invokeChannelInactive(DefaultChannelHandlerContext.java:237) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelHandlerContext.fireChannelInactive(DefaultChannelHandlerContext.java:223) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.ChannelInboundHandlerAdapter.channelInactive(ChannelInboundHandlerAdapter.java:75) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.handler.timeout.ReadTimeoutHandler.channelInactive(ReadTimeoutHandler.java:143) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelHandlerContext.invokeChannelInactive(DefaultChannelHandlerContext.java:237) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelHandlerContext.fireChannelInactive(DefaultChannelHandlerContext.java:223) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.DefaultChannelPipeline.fireChannelInactive(DefaultChannelPipeline.java:767) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.AbstractChannel$AbstractUnsafe$5.run(AbstractChannel.java:558) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:354) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:348) [netty-all-4.0.10.Final.jar:?]
	at Launch//io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101) [netty-all-4.0.10.Final.jar:?]
	at java.base/java.lang.Thread.run(Unknown Source) [?:?]
Caused by: java.io.IOException: Packet was larger than I expected, found 85390 bytes extra whilst reading packet 3
	at Launch//net.minecraft.util.MessageDeserializer.decode(SourceFile:42) ~[ez.class:?]
	at Launch//io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:232) ~[netty-all-4.0.10.Final.jar:?]
	... 16 more

This might be relevant:
0.8.0...0.8.1#diff-0c802d056f7590d659fb2eb647c47de60d6a4a3d31d818a96288b8cf8c200f70L52