Differing behaviour on consecutive runs

[David Jennings]

Hi all. I have a strange issue with sync'ing from a USB-attached ext4 
file system on one machine, to a USB-attached ext3 file system on another.

The sync works fine (a few thousand files). If I run it again straight 
away, or a few minutes later, rsync reports no action required.

But if I wait for a few hours and run it again it copies all the files 
again.

I'm trying to determine what's making it think the files are not 
up-to-date. I have all the debug flags turned on. Am I missing something 
that will let me know what rsync is thinking?

My command-line is:

rsync --info=all4 --debug=all4 -auvz --modify-window=1 ./src/dir/ 
server:path/to/dst/dir/

On the good run I see this in the output:
...
generator starting pid=3205
delta-transmission enabled
recv_generator(.,0)
recv_generator(.,1)
recv_generator(604-001-bg.jpg,2)
604-001-bg.jpg is uptodate
recv_generator(604-001-l.jpg,3)
604-001-l.jpg is uptodate
recv_generator(604-001-m.jpg,4)
604-001-m.jpg is uptodate
...

and on the later run when everything is copied again I see this:
...
generator starting pid=10544
delta-transmission enabled
recv_generator(.,0)
set modtime of . to (1282081725) Wed Aug 18 07:48:45 2010
recv_generator(.,1)
recv_generator(604-001-bg.jpg,2)
recv_generator(604-001-l.jpg,3)
recv_generator(604-001-m.jpg,4)
...

I've just noticed that "set modtime" differs between the two runs. If I 
do an ls now on that directory I get:

$ ls -ld --time-style=full-iso 604
drwxr-xr-x 2 dave dave 4096 2010-08-18 07:48:45.000000000 +1000 604

Sorry for the long post. This issue has been driving me crazy.

Dave.