I was exploring an abandoned mineshaft and came across a formation that I would assume is a set of stairs that generated in a ravine and didn't form a wooden floor.
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I am requesting this to be re-opened. I can confirm that it appears to still happen in the current version (tested in a superflat world).
The issue is a "bug of omission". There used to be no code at all to generate a floor when carving over air. Code was added to force a floor when carving tunnels over air. The issue is forcing floors when carving a staircase over air.

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done; http://www.reddit.com/r/minecraftsuggestions/comments/27nq2z/mineshaft_staircases_and_start_rooms_should_force/ if anyone reading this wants to upvote it.
Requesting review, this is the only mineshaft structure piece to not ensure a floor is present, disconnecting sections if a cave or canyon generates through it.
The world generator does not generate structures of stones for stairs and only flat wooden structures.
Wooden bridges over ravines are in fact generated, but those "staircases" are generated by removing the exisiting stones.