All of the decorative stair blocks added by Railcraft refuse to be moved by pistons. This seems odd because all the vanilla stairs, as well as the full-block decorative blocks the stairs come from, can be moved by pistons.

I'm guessing Railcraft's stairs have a a TileEntity, in which case would it be feasible to implement them without it?

No, if I was to not use Tile Entities, I'd have to use 1 block Id per variant, and there are like 20 variants.

OK, fair enough. I thought you might be able to make the stairs work with one id the same way as decorative blocks do, but I guess not.

Nope, stairs use metadata for rotation information.

This will be resolved when stairs return after the flattening.