I was playing and using flint and steel on a cobblestone wall makes it turn into a corner piece for a second or two. One time it stayed like that for a couple of minutes.
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Confirmed.
Confirmed to be in 13w48b. Happens when the top is set on fire, it appears to be a corner wall for a few seconds.

Still an issue in 16w33a
This issue has been fixed in 17w48a.
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Cannot reproduce please describe in detail how to reproduce.