Unable to write context property in Encode Stage of send pipeline

I have a send pipeline , and a pipeline component which I have added to the Encode Stage. Inside the pipeline component, I use pInMsg.Context.Write method to write a property which has MessageContextPropertyBase.

Now, the send port is suspended due to some problem. In the suspended service instance, I have a message whose context does not contain the property I wrote. I dont know why.

Interestingly, the message associated with the suspended instance is raw (like before Assemble stage) . Why ??