Do Mystery Blocks that turn into Ice Blocks immediately cause you to slide?

tl;dr: If I step on a Mystery Block that reveals itself as an Ice Block, does it count my initial stepping on the block as stepping on a normal block or as an Ice Block?

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While attempting the Obelisk Tower of Babel, I eventually come across Mystery Blocks, which can turn into any type of block once you step on them. Naturally, they can turn into Ice Blocks, which cause you to slide until either hitting a non-Ice Block, hitting a wall, or sliding straight off the edge (you don't catch yourself on the edge of an Ice Block you slide off of).

However, a few times now, I've had a Mystery Block placed at the end of a row of blocks, run towards it with the intent of jumping off once it reveals itself, but instead sliding straight off the edge to my death once it reveals itself as an Ice Block. It doesn't happen often (luckily), but it's certainly frustrating as it doesn't really seem fair, since I had no way of knowing what type of block it would be.

That said, I'm unsure whether this occurs simply due to the Mystery Block being an Ice Block or if the registered a second input after stepping on the Ice Block. Is the Ice Block slide being determined when I step on the Mystery Block before I know it's an Ice Block (meaning I should have dropped down and hung to reveal the block type) or is a second input required to make me slide on an Ice Block? For a regular Ice Block, stepping onto it will cause you to slide. Is that how it works when the Ice Block was a Mystery Block when it was stepped on as well?