Question on trade-ins after elimination

If you eliminate someone, and you get their cards, aren't you supposed to be able to trade in? I did this in two flat rate games today and it wouldn't let me. Does it have to be a mixed set?
Conquer Club, a free online multiplayer variation of a popular world domination board game.
http://www.tools.conquerclub.com/forum/
http://www.tools.conquerclub.com/forum/viewtopic.php?f=6&t=17395
dolemite wrote:Thanks for the answer. Doesn't it seem like if you have enough for a trade-in, it should work?