Falling from Block while Sneaking

What I thought what happends:
When I am Sneaking on A Chest, I will Always on The Chest, until I release the Shift Button.
When I am Sneaking on a Block, I will Always on The Block, until I release the Shift Button, when Snow/Redstone Repeater/-Comparator next to the Block is.
What really happends:
I Fall from The Chest, And, I fall on the Redstone Comparator!
Screenshots: