The water goes inside the block when I want to play it on the block and when I get it when I use my Empty bucket on the block when it's inside
I know that it happens on slabs,stairs,hoppers
I think that it happens every non full but I'm not sure (didn't test it on all of them)
Thank you for your report!
However, this issue has been closed as a Working as Intended.
https://minecraft.gamepedia.com/Waterlogging
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