Question about the diacetyl rest process

When producing beers that must have a "clean" / "neutral" flavor like lagers, usually the fermenting temperature is low to prevent off-flavors to show. But then, is recomended to apply a diacetyl rest in order to reduce the buttery, butterscotch-like flavor to beer that the diacetyl provide. Here's the part I don't understand. You do a lager fermentation at lower temperatures to prevent off-flavors, but to do a diacetyl rest you raise the temperature from about 50° to 55° F to 65° to 68° F. What's the explanation for that? Isn't raising the temperature causes the yeast to produce undesired flavors to the beer? I don't get it!