All mx.core::xxxAsset are related to the "[Embed ...]" directives. Any resource which gets
embedded will be represented as one of MovieClipAsset, MovieClipLoaderAsset, BitmapAsset and so forth
[1]. There is also a compiler option for mxmlc to not remove the generated action script code
("-compiler.keep-generated-actionscript"), so you can inspect what is actually generated. This
option can also be changed in flex-config.xml, look for<keep-generated-actionscript>.
[1]
http://opensource.adobe.com/svn/opensource/flex/sdk/trunk/frameworks/projects/framework/src/mx/core/
So they question remains, why does the Preloader cause the runtime to
instantiate something from the
"mx.core" package, and why did it not used to do that in earlier version of
the flex compiler and
framework .swc libs.
