Dave, That, and the yeast can get caught up with the trub. Have read that the Germans will let the trub settle out in a settling tank for 24, rack of the trub to the primary fermenter, and then pitch.
Jack. I do the starters in the basement, about 60-62F. If you think about 6L for 10 gallons, that is a lot of liquid that is not the same as the beer you are making going in. I pitch cold to minimize the VDK production. The yeast fired off immediately after they were blown off the bottom with CO2, with a bubble going through the airlock every second, and are still going along nicely at ~49F.
Yeah, my lagers usually get going fairly quick. This has happened twice. I think next time I will wait 24 hours, dump the trub, and then add theO2 and pitch the yeast.