After looking briefly at the API docs, I noticed that there are duplicates of several of the filter classes with the same name. For example, there is a DropShadowFilter in the spark.filters package and there is another one by the same name in the flash.filters package.
After looking at the source for the DropShadowFilter in the spark.filters package, it appears that the filters in the spark.filters package are basically just wrappers that return their flash.filters packaged equivalent from the clone() method. I’m guessing that they just wanted to create filters that fell inside the spark package structure that could be improved or extended at a later time. You can easily replace this:
<s:DropShadowFilter /> with this:
<mx:DropShadowFilter /> and get the same result.
Any one have a better explanation?