Ice does not generate on waterlogged blocks

I was designing an ice farm, but something surprised me: ice wasn't generating next to waterlogged trapdoors. I found this unusual because before I started making the farm, I tested if ice would generate next to trapdoors, and it did. Only then, they weren't waterlogged. to prove that this was a problem with waterlogged blocks, I did the same test with stairs, both waterlogged and normal. Same results as the trapdoors, even when the full block side of the stairs was against the water source. This really doesn't make any sense to me, and it doesn't feel intended.