When standing on a lower half slab a player can jump on a chest (and some other blocks) with a block below that is one block above the slab's position.
All blocks i found this to work with are in the screenshots.
The player first starts falling a small distance but then climbs on top of the chest similar to climbing a stair/slab.
Since the height difference is 1.375 blocks and according to the wiki the player's hump height is approx. 1.252 blocks, this should not be possible.
I also tested it on a Server and it worked.
It didn't work on the end portal even though it is visually smaller that the chest.
I tested it on older Versions and it seems like this bug was introduced in release 1.8.

I found another issue that was essentially the same but it was resolved with "Cannot Reproduce" https://bugs.mojang.com/browse/MC-117465