weegraeme The key here is the 31 hours stop in DOH. You must collect your baggage in DOH and re-check it again for the next leg of your ticket. In the eyes of IATA, whose baggage rules apply to your tickets, you have broken your journey and the rules are applied to the separate parts of your journey. If there is a shorter connection then this will certainly be the case.
Some airlines ignore this rule and allow access to your baggage during the stopover without regarding as a separate journey. QR is not one of them!