Can't swim under stairs if there is solid block on them.

I found out that you can now swim through small tunnels, so I made a tunnel out of stairs above ground and it worked. When I had solid blocks above it, it didn't let me swim through. It does work when there isn't a solid block above it though (like slabs or stairs)

Edit: Found out it doesn't have to be made of stairs. A normal block tunnel will also cause this glitch.