This is a strange glitch in World 3-6, where Mario will temporarily be unable to break a Brick Block. This takes place at the section with an Ice Block on top of a Donut Lift and two Koopa Troopas, one on the upper platform and one on the lower platform. Get to the lower platform, where a Brick Block containing a Super Leaf sits. Kick the Koopa into the block (or tail-attack it) to release the Super Leaf. If you collect the Super Leaf while it is rising, you won't be able to break the Brick Block directly above you for about four seconds.

Note: This glitch also happens if small Mario collects a Mushroom from the block, but you'll only have about 1.5 seconds after the Mushroom spawns to grab the Mushroom and jump. (Special thanks to Vorpy for the technical analysis.)