why is the download manager weirdly erratic at times?

[Robert P. J. Day]

   occasionally (possibly only at times of high network traffic), the 
download manager is strangely erratic in that the amount of data 
listed as being transferred bounces all over the place.

   at the moment, i'm doing a regular download of FC3t3's disc4 ISO 
image.  using "ls -l", it seems that the size of the downloaded file 
is growing normally, but the amount transferred in the download 
manager is bouncing around from 22xxxK up to 39xxxK, then back down 
again, then up again, and so on.  and the progress bar is matching it 
in weirdness, growing suddenly, then shrinking again, and so on.

   anyone else ever notice this?  any thoughts on what it means?

rday