I followed the instructions in this page
and wrote some code for downloading a file. I noticed the behaviour you mentioned(half a second instead of smooth) occurring whenever i downloaded the same file a second time. The first time download was smooth. This was in firefox. In IE, it jumped to 12 % in half a second. So I concluded it was because of the browser cache. Do u have similar behaviour or does it occur during the first download too?
my problem is in FF where the progress event gets called once and then never again, even for 22mB file
I've used a file reference class and attached an event listener for ProgressEvent.PROGRESS to it. Can u clear the cache and see if the behaviour is repeated. Could you also let me know if you are using the URLloader class or the Filereference class the way it is detailed in the link i posted previously.