I've noticed glowstone blocks randomly disappearing (visually), which is pretty persistent between re-logs and client restarts (on server). It is apparent from usually just one side, and always seems to be the glowstone blocks. Screenshot is just a partial block missing, but it does happen to the whole block.

Do you have optifine?

I do, and haven't so far been able to repeat it after reloading the pack without, but it was pretty random. What about Optifine would only conflict with Chisel blocks.

Optifine is closed source and changes many unexpected internal functions without warning, so it's become general practice to either replicate the fault without Optifine, or take it up with the Optifine Dev