netty: ctx.writeAndFlush throws BlockingOperationException even channel handler is in separate EventExecutorGroup

Expected behavior

BlockingOperationException only need to be thrown when calling await inside IO thread

Actual behavior

This is exception is thrown even when doing this:

ChannelInitializer(){
      initChannel(...){
           addLast(....)
           addLast(eventExecutorGroup,"businessExecutor", new SimpleChannelInboundHandler(){
                 channelRead0(...){
                        val p = ctx.writeAndFlush(msg)
                        p.await()
                 }  
           })
      }
}

Steps to reproduce

Minimal yet complete reproducer code (or URL to code)

Netty version

4.1.36

JVM version (e.g. java -version)

OS version (e.g. uname -a)