Context and Send Ports

I have a pure messaging based solution (no orchestrations), that
contains maps in a send port.
In the receive adapter, I set some context properties to be used later
to route the reply message back to it's source. During the mapping
process, my custom promoted properties disappear. They are present in
the source message and missing in the destination message. Granted,
there are other properties missing as well, not just my custom ones.

How can copy my custom promotions when I map the source message to the
destination message?

Again, I do this without orchestrations.