Have a suspend option in word list
Sometimes you have a relapse in studying and want to start out new again on some fresh texts but not have the old words come back at you in the flash cards until a later date.

I’m thinking about changing the scheduling system slightly to prioritise newer words over older ones for this reason.
I’ve noticed this myself and also in this Readlang review Ron says that he periodically deletes all his cards to avoid the same problem: http://www.languagesurfer.com/2015/01/14/readlang-review-six-ways-to-get-the-most-out-of-this-awesome-tool/ – when I read this I knew that something needed to be fixed. Thanks for reminding me about this!
One thing you could try in the meantime is:
1. Read a text on readlang.com (as opposed to the Web Reader) and translate a lot of words.
2. On the flashcard page, there’s a “Study from…” selector – use this to only study words from the recently read text.