This happened during multiplayer with the server Nexuiz 2.5 and me running nexuiz-glx 2.5:
After I got killed, I respawned "dead"/in spectator mode - no weapon, no HUD, score table visible and I was able to move through walls/ceilings. I don't know if my player model was visible to the other players, however, I got killed (death sound effect, "fragged by" message) again (probably by a stray nex beam - hard to say if the killer actually saw something to aim at) when my view was about halfway into a wall. After that I respawned normally and was able to continue playing as if nothing had happened. This all happened twice in maybe 10 minutes. The map was aggressor, my ping was pretty much stable throughout the game at around 50ms and framerate maybe 30 - 75, depending on the scene being rendered. I don't expect anybody to really look into this since it seems so random and I don't know how (to even try) to reproduce it, I just thought you'd want to know.
My system: Ubuntu 8.10 with 2.6.27-11 kernel, Intel Corporation Mobile GM965/GL960 with latest 3d-compatible drivers (I'm play on a laptop.)