I'll briefly explain the images, because they tell the story better. The 01 image is the setup, two cases. One with a wall with the height of two blocks, the second case (the one with a lapis block) with a height of three blocks. I have only put that ONE lapis block, to signify which block is the "troublemaker".

In the case of the 02 image, pressing against the wall, walking up the stairs nothing weird is happening, you walk unhindered up the stair.

In the case of the 03 image, pressing against the wall, the block positioned as the lapis block is most likely being calculated as an obstruction for your head going up, so you stop dead and can't move past unless you start looking more to the right - at a certain angle you will move up the stairs.

Walking up a spiralcase of stairs and you keep to the outer wall of it, you'll end up stuttering and getting a bit stuck.