Quest icons and NPC names disappearing

In crowded areas, quest icons over NPC heads and their names are disappearing, even when targeted. It seems to have something to do with on-screen culling, because I can be watching a quest icon and when enough PCs enter my field of view, the icon disappears. When enough people leave the field of view, the icon returns. Can also get it to occur if I rotate my camera around at different angles (possibly bringing too many models into the field of view). None of my graphics settings seem to change the behavior.

Anyone experienced this and found a fix?

The icons on the map are disappearing also, though not necessarily at the same time as the icons over NPC's heads. Even the aethernet crystals are popping in and out on the map!