camel-mail problem : headers lost (more info, maybe bug ?)

[Joël Guelluy]

Hello,
One week ago, i previously tried the question here. Now i have more 
infos...

Sample code and explanations : 
https://stackoverflow.com/questions/73948864/camel-frommail-loose-headers

Short version :
Sample Route

from("imap://server?username=aaa&password=bbb&copyTo=out&delete=true&unseen=false&folderName=in&mapMailMessage=false")
     .setHeader("copyTo", simple("works"))
     .bean(MyTest.class, "hardcodeJson")
     .unmarshal(new JacksonDataFormat(Reply.class))
     .log("copyTo=${header[copyTo]}")

The problem : in console, i see in .log() that the content of the 
header[copyTo] is lost.
if i comment the .unmarshall(), it's OK
If i replace the from("imap") with a from('direct') in an unit test, 
it's OK.

Can someone explain me why ?
Is it a bug ?

Thanks in advance...