"Bizarre Error" message from apt-get

[Ross Boylan <ross@biostat.ucsf.edu>]

apt-get update gives me (at the end of the downloads)
W: Bizarre Error - File size is not what the server reported 189 191
W: You may want to run apt-get update to correct these problems

I saw this on an update from about 7 hours ago, and again just now.
Which kind of undermines my original theory that this was a side effect
of an archive update.

Both machines are using Berkeley's mirrors, though I have other entries
in sources.list.

Any idea what's going on, or how to track it down?

-- 
Ross Boylan                                      wk:  (415) 514-8146
185 Berry St #5700                               ross@biostat.ucsf.edu
Dept of Epidemiology and Biostatistics           fax: (415) 514-8150
University of California, San Francisco
San Francisco, CA 94107-1739                     hm:  (415) 550-1062