Sometimes this game will decide it doesn't want to listen to my controller seemingly at random. In this video with input display, I'm holding left on the straight piece, and it just stops for no apparent reason. Spamming left when I see it stuck doesn't help either.

I get why some things don't work, like quarter-circling from left/right to down will make the piece not drop, but I can't figure out what causes this. Help would be appreciated.

A couple of us have noticed the same bug. Although not shown, you probably had stacked a piece with blocks above the top most part of the screen; and those "rogue blocks" are actually there even though they aren't shown.

For instance, if you have 3 lines of space at the top, and put a 4 piece upright; that means 1 block was above the screen. That 1 block becomes rogue and will continue to block you even though you don't see it and have made space later on.

So that block you're hitting is you trying to push a piece into the rogue block. Eventually it will clear up (I think, though I haven't exactly figured out when it clears) however it's usually a run ender.

Oh, wow. That's exactly what happened. Thanks!

@sYn: "Eventually it will clear up (I think, though I haven't exactly figured out when it clears) however it's usually a run ender." <-- The orphaned blocks are there for the rest of the game, I'm afraid. The only thing that resolves the issues somewhat is that you're less likely to bump into them when the gravity increases. In that sense, any garbage in the vanish zone stops being a problem once you get far enough into the game.