I've never seen this, myself, and this is the first report I've received about it. What version are you on, and what mods are you running?
I currently use optifine and rei's minimap, and that graphical glitch appear since i used it on 1.4.5, when i first used this texture pack, which was 1.2.5, i never had the problem, and i have used the exact same mods. I will try see if there is any difference if I remove those mods.It seems that that fog is restricting my vision to see the "glitch", due to optifine removing those fog I was able to see that hole in the sky. Other texture packs do not have the same results... weird :/
@zinclock I know this may be a stupid question but are you using Optifine? If not I would recommend you using it. I have a laptop that can't handle intensive stuff as well, but with the help of Optifine I could run Minecraft at an enjoyable FPS. Having Minecraft on short or below render distance helps too ;P
@seanfletchr Will you be adding fire fireworks particles in the next texture pack update? (Woohoo 2 stupid questions in 1 post! New Record! xD ) On another note, will mobs have a custom texture soon? other than the original ones.
Is that the trapped chest? or the normal chest re-textured?