You can place Lilly pads only on top of empty water block, and you are unable to place them on top of water block occupied by kelp, corals, coral fans, sea grass, sea pickles, or any waterlogged block.
In Java edition you can place Lilly pads on top of the said blocks. So I presume this is how it is intended to be.
Cleaning up old tickets: This ticket has not been updated recently (~1 year+) so is being closed as Cannot Reproduce. If you feel this is still a valid issue then please comment, or create a new ticket following the Issue Guidelines.
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