JSF core doesn't have an upload component. Please provide the JSF markup so we can see what component you are using to do the upload. If you can attach a simple app that demonstrates the problem then that would help a great deal.
I am also involved in this activity with Arun.
We are using the tomahawk <t:inputfileupload> component to upload the files.
We find that the file is corrupted before our application reads the file from this component.
tomahawk jar version used is 1.1.8
You need to get help from the Tomahawk project. JBoss AS doesn't have anything to do with the tomahawk file upload compoent.