Maps in item frames show shading problems

The bug

Maps placed in item frames show some strange shading problems, depending on their rotation:

18w21b, 18w22b and later:

• Not rotated: All map pixels appear normal, but banner marker icons are shaded dark
• Rotated by 90 or 270°: Everything looks normal, unless you move your mouse over an inventory item (which causes dark shading of the map)
• Rotated by 180°: All map pixels and icons are shaded dark except for banner marker icons

18w22a:

• Not rotated: All map pixels appear normal, but banner marker icons are shaded dark
• Rotated by 90°: Everything looks normal
• Rotated by 180°: All map pixels and icons are shaded dark except for banner marker and map position arrow icons
• Rotated by 270°: All map pixels appear normal, but map position arrow icons are shaded dark

This issue is almost certainly an unintended side effect of the fix of MC-72866 in the previous snapshot.