I had a couple instances of this happening in standard and in Brawl. I had some cards that had me select a card like fetch quest for example that had me mill 7 and select a card from the milled cards. It did the game action and I had 6 lands a sorcery milled and it froze at that point, not letting me pick any of them and ending my turn. I had this happen again with a search effect on the top of my deck. It wouldn't let me select any cards from the top of my deck to add to my hand. This was all in Brawl, but then in standard, I was simply unable to manifest dread. It didn't even give me the option but I could see the top 2 cards of my deck to make the choice.