rsync transferring same files every time?

I just got rsync running on my Windows 2000 machine. I'm using it to
update from my windows machine to a Linux server. Everything seems to
work ok except for one wierdness. As far as I can tell, once rsync
uploads a file, it always uploads it in subsequent calls to rsync.

So, for example, say I modify the file regtest.pl. When I run rsync (in
verbose mode), the response looks something like this:

rsync: building file list...
rsync: 450 files to consider.
Lib/Joyis/Apps/Event.pm
Lib/Joyis/Apps/Recovery.pm
Lib/Joyis/CommandLine/regtest/regtest.pl
wrote 9264 bytes read 824 bytes 2241.78 bytes/sec
total size is 1963394 speedup is 194.63

Now, suppose I then modify Util.pm and run rsync again. I get something
like this:

rsync: building file list...
rsync: 450 files to consider.
Lib/Joyis/Apps/Event.pm
Lib/Joyis/Apps/Recovery.pm
Lib/Joyis/CommandLine/regtest/regtest.pl
Lib/Joyis/Util.pm
wrote 10026 bytes read 870 bytes 3113.14 bytes/sec
total size is 1963400 speedup is 180.19

Notice that regtest.pl, as well as some other not-recently-modified
files are in the list of uploaded files. It looks like rsync is
continuuing to upload the files even after they've been uploaded. I
checked on the server and the files do get modified, so I don't see why
rsync if uploading them again.

Why is rsync behaving in this manner? Is there some configuration I may
have missed?