The calculation of taxes is completely weird. When trying to book Europe-YUL return itinerary the taxes for the outward trip initially are displayed at appx. 150eur and 45eur return (clearly, without fuel surchage). However, when you proceed further you see the total amount of taxes at apprx. 300 euros, so fuel surchage for the return trip is also included.
However, if you try to book the mirror-trip YUL-Europe, the situation is upside down - the final total of surchages is lower than previously displayed and does not include fuel surchages on either direction (total appx. 100 eur).
Same issue of non-availability of Promo awards when booked as one-way on YUL-Europe direction, but they are available if booked as a part of the roundtrip.