jQuery UI Progressbar Plugin Issue

jQuery UI Progressbar Plugin Issue


I have been trying to use the progressbar plugin, but have had no
success so far. The problem is that it would not refresh the current
percent while the heavy back-end process is still running, only when
it reaches 100%. It means the progressbar goes from 0% to 100% without
displaying values in between (25%, 50%, etc). Maybe I am missing some
sort of flush method.
The back-end process is triggered by an AJAX call via MPAJAX plugin. I
had to make use of multipart response messages in order to get each
percent update individually. Otherwise, it seems that the AJAX handler
groups all updates in a buffer, then release them all together.
References:
Progressbar Plugin: http://jqueryui.com/demos/progressbar/
MPAX Plugin: http://plugins.jquery.com/project/mpAjax
You can also find my tiny source-code at http://pastie.org/624640 --
This is just a proof of concept. Please have a look at the progressbar
update at line 13, and the AJAX call at line 19. Am I doing something
wrong?
Thank you very much in advance.