For years now, this bug has been around. It affects the latest beta too.
The [progress] section, will 'lock-up' when you submit a file to upload. I have seen it happen in all browsers, and all templates.
It prevents reliable file progress
I tried to create a progress bar with some JavaScript, and even that just 'stops' after the first or second request.
Maybe it is unavoidable, maybe it is a bug with HFS. I dunno, for now I have just opted for an image that makes it 'look like' something is happening. But to get accurate feedback this is an issue to overcome. In the past I have included file progress, but the only information I or anyone else really wants to know, is upload progress, and without being able to request it every second or so, to get an updated figure, its not very useful!