This is most likely caused by the new pane/iron bar rendering which makes them a 2 pixel thick "box" rather than a super thin pane with a two pixel thick edge.
*note
I have searched to see if there were any other pages about this bug, and haven't found any
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is duplicated by 6
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I can confirm as well. It seems that on straight lines of iron bars running north and south, the norther most piece does not render correctly.
Can confirm.