I've had this same issue your talking about, except with road bike derailleurs Ultegra, 105, and Tiagra. Far as I know Deore is a MTB group set, and is designed to work on a triple crack set, maybe Shimano didn't list the road crank you have not thinking it would end up on one. But as you noted it is working, do you really need a 52 anyway ? I realized yesterday that I'm never going to need the 50T front, and 11T rear I have in this lifetime. I have a base line Deore shifter on my front crank, with a Tiagra 10 speed derailleur & a 50-34 compact crank. (Sram Rival), this setup came stock on the 2013 FX 7.6.. And it sux's at shifting, have had 5 different mechanics looking at it, and only one could make it shift half ass, about the same as I could get it with hours of adjusting. In my opinion TREK screwed up and installed a Deore MTB shifter, on a 10 speed road derailleur that is compatible with a compact crank. Here is WHAT should have came on the bike : http://www.amazon.com/Shimano-Tiagra.../dp/B005LKXA4W and I will be ordering one. Why do you only want a double crank, less weight ? Given everything is working correctly, and if you never use the 52 front with the smallest rear. Just replace it with a 48-38-28.. (not knowing your rear cassette size). In theory your current set up would not work with a double road crank , from my experience.