Copying Layer Styles Changes Parameters

Why is it that sometimes when i drag copy (hold alt and click and drag) a layer style, specifically drop shadow, some of the parameters change? It doesn't happen every time. Sometimes the drop shadow is exactly the same as it was on the other layer. But sometimes the parameters like distance/size/spread get raised a handful of notches making for a different looking shadow unless I go back in and lower it back down manually to match.