As demonstrated in the Showcase
http://showcase.richfaces.org/richfaces/component-sample.jsf?demo=fileUpload&skin=blueSky
So we can add multiple files. When the maxFilesQuantity is reached. The "Add" button is removed. This is good.
But after clicking the "Upload", the "Add" button reappears. Seems to be a bug.
Is this the same with your problem?
[RF-12366] Uploading 2 files despite rich:fileUpload:maxFilesQuantity="1" - JBoss Issue Tracker