Yep it's not a bug!
It's part of a plugin we have (i think PS?) because it only works inside a PS field
You can also rotate stairs, logs, slabs, and pistons! (you might be able to rotate more stuff but those are the only ones i've ever tried XD)
If you right-click a slab, it will flip it up or down.
For stairs, shift+right click will flip it up or down, and just plain ol' right-click will turn it north/south/east/west :3 super useful stuff!
it's weird though, because the "new" blocks (acacia & dark oak) don't like to rotate for me :T this means both stairs, slabs, and logs T.T bleh