When we drop a sand on top of a shulker the sand stays inside it instead of dropping it

I think it's normal because the shulker isn't an actual block. And if you drop two sand blocks it'll teleport away.

As of 1.0.0.0, sand (and other falling blocks) no longer fall inside the shulker and cause it to suffocate. Instead, the sand falls on top of the shulker and remains in falling-block-entity form indefinitely (since it never lands on an actual block).