In Survival Multiplayer, glowstone at times will not emit light unless I walk near it (within what would be the light range), or in some cases if I put a block attached to it and then destroy that block (sand, dirt, anything works).
I built paved stone brick roads with glowstone embedded in the middle of intersections, and I also have glowstone "streetlights", which are just glowstone blocks atop fenceposts. This bug affects both. It seems to be completely random which blocks will work each time a chunk loads. The chunk might load one block's lighting normally, while another is out. Then I can close out Minecraft, reopen, and the two have switched, or both are on, or both are out. It happens all over my world, not just in one area.
This does not appear to affect glowstone in the Nether. It glows just fine there.