In Defend Missions I never get the warp crystal and other rare resources they promise. It happened to me on different games so it's not just a one time bug.
Love the game it keeps you challenged, at first your trying just to finish the level, and unlock the new levels, after that you try and get all challenges and than you try to get as high as you can in the score list. my score 10900 game rating: 5/5
 "Arkandian Crusade"){kind=icon}
 "Blosics 2 Level Pack"){kind=icon}