When a MultiFileUploadInput is used in a WizardStep, the files queued for upload are silently ignored when the Upload button is pushed.
An example application is attached.
Simply download, extract, compile (mvn package), deploy, and follow the instructions on the page.
There are two examples: A working on where the MultiFileUploadInput is used on a separate Page,
and a b0rken one where it's used in a WizardStep.