You are right Squirrel. "Loading up" happens when the engine is idling, because the engine isn't burning the fuel fast enough to prevent the oil in the fuel from starving the engine. Another problem with an engine loading up, is it causes the engine temps to fluctuate more. The oil is what cools the engine while running. When idling, the oil buildup cools the engine slightly. In general, a well tuned engine should be able to idle for at least 5-10 seconds with minimal oil buildup and still be able to get a good start.

The higher your oil content, the easier an engine will load up. Oil is the only property in the fuel which DOESN'T ignite. That is why the side of your buggy/truck/car has an oily film after running.