I actually encountered something similar during a trip to South America in the early '80's. All the U.S. tv shows were dubbed into Portuguese. Some cartoons I saw you could still hear the original voices very faintly.
My theory is that in some instances they don't have a clean music and effects track to work with, and the English voices are being filtered out.
I also discovered that Scrappy Doo is an annoying character in any language. ;)