When an Elder Guardian tries to use its “curse” (that should show the Elder on the screen and apply Mining Fatigue III to the player), the game starts to play the corresponding sound, but then everything turns into a single color (light blue in my superflat world, brown in my normally-generated world). The Mining Fatigue III effect is still applied, though in 1 of my 2 occurrences of this bug, it wasn’t saved (nothing was saved at all that time).

This happens with both naturally spawned Elders (in temples of the sea) and Elders spawned with the /summon command (/summon Guardian ~ ~ ~

).

In 14w30c and older, the curse works fine.