Does studying flashcards, both front to back and back to front, decrease retention opposed to only memorizing one way?
No, it just makes the intervals suboptimal. Either bury the card if the opposite side came recently or change the card to the direction it will usually appear. (Sometimes it will be the description first.) The forgetting curve, memorizing right at the periphery, will still go back up: 


There is also the study done by Glenberg Smith &amp; Green about this...

Anki is programmed to deal with similar "sibling" cards
The algorithm will bury them--except when learning...


https://www.quora.com/topic/Spaced-Repetition
https://www.reddit.com/r/Anki/
https://anki.tenderapp.com/