JerseyServerHandler uses the same NettyInputStream across all messages and if a request does not close it's entity input stream a chunk of it's data will be visible to the next request on the same channel.
The handler tries to reset the inputStream between messages by calling nettyInputStream.clear
https://github.com/eclipse-ee4j/jersey/blob/master/containers/netty-http/src/main/java/org/glassfish/jersey/netty/httpserver/JerseyServerHandler.java#L83
However clear does not fully reset the NettyInputStream. It does not null out buffer or current so the next call to read will return data from buffer which is data from the previous call.
Clear should be fixed. It should null cause, reading, buffer, and current. It may be appropriate to notifyAll and cleanup buffers in isList. You could also or instead allocate a new NettyInputStream instead of reusing the same.