JMSMessage vanishes attachments

When using this kind of route
<from uri="activemq:queue:test"/>
<camel:process ref="mailProcessor" />
<to uri="smtp://localhost:25?to=user@localhost" />

and trying to enrich the message in the mailProcessor with

exchange.getIn().addAttachment("attachement.txt",
new DataHandler("Hello world", "text/plain"));

The received mail doesn't contains any attachment.

If the input "from" is a "direct" instead of activemq, it works fine.

Inspecting source code, MessageSupport.copyFrom(Message that) does
getAttachments().putAll(that.getAttachments());
but the child class JmsMessage doesn't.