Images for drops changed to ?landscape pics?

Was playing, got a Skype call. Came back to game and when I dug some sand the pieces were shown as floating, revolving 2D landscapes instead of their usual. Shadow still present. I could collect as usual. The rotten meat from a zombie kill displayed normally, but the cacti also rendered with a new image - this was more distorted & unidentifiable. Both the new images were consistent for their item, once changed.