Beacon lights disappear when looking directly at them

When you stare directly at the light beam at Y56 or above it can not be seen. Tilting your head down will make the beam appear, but it will disappear again when your head is lifted.

The beacon is located at Y10 on a 4 level iron pyramid (if that helps?)

I copied my world to older snapshots 14w34d & 14w33c and can confirm that the bug is not evident in 14w33c, but is in 14w34d.