I've also just found that you can grab block but can't ungrab it to grab another one. When I tried to click on the the same block to put back I just pickup new one and throw previous...
ya that sounds about right. you should drop the block when you are holding a block and click. there is no check to see if you dropped the block in the right spot.
there is no ungrab feature it is up to you to grab the blocks in the right order
