Erich, could you try removing this 2 objects (gemglcleardeph and gemglclear) from the gemchain and tell us if it's working better? (do you also nead to destroy and then create the gemwin again?)
when i remove them and reconnect the chain i still dont see anything. i have to close the window and create it again. it behaves like you describe (but only with my nvidia with ati osx it works like chris says).
i dont understand your question about if it works better ? i just works as normal single buffer then.
best
e