Hi Renatas,
I had the same question as you and I think yes, there should be P/L-postings for the principle amounts due to FX-valuations. Otherwise it would be possible to transfer profits between different periods at least, even if FX-rates remain constant. However I have reported a problem in another thread with that FX-valuation:
http://scn.sap.com/thread/3480479 Have you implemented the note successfully?
Regards, Sebastian