rsync to fat32 on different platforms

[Andreas Nef]

I have a dozen of external usb disks which should be kept in sync with  
a central rsync server.
As I can't predict which OS they will be used with they are formatted  
with fat32. If I use them with either Linux (ubuntu) or OS X rsync  
works without problems. However, when I try the syncing with the hd  
attached to a windows pc the rsync process (using cygwin) will take  
close to 40 minutes only check what needs to be updated. Does anybody  
know what could be the cause for this strange behaviour? Is it  
something with permissions (parameters I used for initial creation of  
the copy were "-rtluvz --modify-window=1")? Or are there compatibility  
issues with rsync/cygwin?

Thanks for your ideas, Andreas