When you place either a slab or a stair on a block, sometimes the server puts it in an incorrect placement. For instance, if you place it in upside down by clicking the upper side of a block, but almost at the bottom, the client will show it correctly for a second then the server will correct the client. I know this is a bug because it is possible to place an upside down half-slab on the side of a right side up half slab.

I have not reproduced in 1.4.4 yet.