The autoUpload feature wasn't targeted for 3.3 (ICE-6637), but at some point it was backported when backporting the support for Servlet 3 multi-part uploads (ICE-9273, r40315). This commit also included some code for the multiple file upload mode, even though it wasn't targeted for 3.3 either. The 'multiple' attribute also exists in 3.3 but it causes an error when trying to use it.
The autoupload issue is easily fixed by simply reverting the Javascript code to a simpler script that was used before supporting multiple file uploads. However, the 'multiple' attribute would stay there, potentially causing issues. We could simply remove that attribute or we could try and add support for the multiple file upload mode, which would require backporting ICE-6204 and all subsequent fixes and improvements to the multiple file upload mode.
To reproduce set autoUpload=true on the ace:fileEntry component.