There's a rendering bug that is affecting stairs and redstone wiring and possibly more.
It appears to be cardinal direction dependent, it seems as though the rendering isn't reading the UV mapping correctly.
Image's are attached to this post including F3 data for the purpose of checking orientations.
If I come across any more objects displaying this bug I'll add images of them to this ticket also.
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STOP IT ALREADY! This is a dupe of MC-66970, and that will be resolved in the next snapshot.
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nice description, though.
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Apologies I hadn't noticed that there was a report for it already as when I searched for "render" it didn't show any reports that were relevant to what I was seeing ingame because everyone seems to be using "distorted" "messed up" "broken" etc.