Stone blocks disappear after breaking - cant collect

I just got the demo version and so far was about to buy until this problem began to appear. It fixed itself when i loaded the game on my first try but after that it didnt go away. I noticed it only happens with any rock blocks, I can collect dirt, wood, and grass etc. These blocks just vanish after i break them (I cant see the collectible icons) and it has happened in more than one area. Would love to hear a solution.