Animated sun texture does not work

The bug

For some reason, if an animated texture is supplied for the sun, this animation will not be present in-game, even if the animation is otherwise valid.

How to reproduce

A resource pack which provides the same animated texture for both glass blocks and the sun is attached to this ticket.

1. Download and apply
2. Look at glass
3. Look at the sun

Expected results

Both would be an animated alternating checkerboard.

Actual results

Glass appears as expected. However, the sun does not appear animated at all.