TL;DR command blocks landing as falling sand entities would run their command if they had the auto:1b tag in their TileEntityData tag, and as of snapshot 15w35c they no longer do this. World is attached, run it in 15w35b/follow instructions then redownload/follow instructions again and try to run it in 15w35c/d/e and notice how it doesn't work. If uploading a world is bad I'm sorry please remove it or get rid of this post.

TL:
This may not be seen as a bug, but those who have experimented with this soon-to-be extinct feature of command blocks will likely see how great it is - kinda like BUD switches. I found while experimenting in snapshot 15w35(b) that if you summon a FallingSand entity of a command block, with the tag "auto:1b" in the TileEntityData tag for it (which affects the tile entity of a block for those who don't know), the command block would run its command at least once upon landing, or attempt to at least once upon landing. What's more curious is that you could stack these command blocks together by making them riding each other with the "riding" tag and they'd still run as long as they had auto:1b, which allowed for easy checks with testfors/chain command blocks, etc. To try this out in a simple way, put this command in a command block in your chat in a creative mode world while playing 15w35b and run it (you'll need cheats on of course):

/summon FallingSand ~ ~2 ~ {Time:1b,Block:command_block,TileEntityData:{auto:1b,Command:"say woo!"}}

if you try and do this in version 15w35c it won't work.

I am including a world download to show a creation involving a command block that will "move" and "turn" when a wool block is "in front" of it. If I had to use redstone blocks to activate the command blocks it might not be possible. This isn't intended to be a "look what I did!' but a demonstration of chain command blocks running when interval ones land with auto:1b and checking conditions in order. Just load the world in 15w35b, follow the directions, then download it again and load it in 15w35c-e and notice how things don't work.

Thank you for the consideration. I apologize if I have wasted anyone's time. I didn't want to let the loss of this possibility to go unnoticed.