Why do error bars on bar graphs seem asymmetrical?

When you have a bar graph with thick borders, the error bars can seem asymmetrical. The distance the bar sticks above the border exceeds the distance it goes below the border. This is because the border is entirely (since Prism 7) inside the bar. The top of the bar border is exactly at the right position to align with the appropriate Y coordinate. (In Prism 6 and earlier, half the border was inside the bar and half was outside; with a thick border the Y value appeared to larger than it actually was.) With Prism 7 and later, the distance the error bar sticks above the top of the bar equals the distance it sticks below the top of the bar. But part of that second distance is within the border.  So the two red arrows below are not equal in length, but they shouldn't be. The error bars are symmetrical around the top of the bar+border.