git performance after directory copy

Hello all,

while moving a project directory around I stumbled over an interesting
phenomenon. On a copied source directory "git status" seems to be about
3 times slower than on the original directory. Only after a "git reset"
both copies behave the same again. Is this connected to the timestamps
of files & directories? Actually I would like to move the project
directories of several software developers to a new partition and
forcing them all to "git reset" in all of their repos is a little bit
annoying. Any suggestions how to "repair" the repos less intrusive?

Here's how I measured. The trees reside on an ext3 FS. I have lots of
free RAM, so after the first operation all further "git status" seem to
run from FS cache in RAM.

$ git clone <path to your preferred kernel>
$ cd kernel
$ time git status # several times!
...
$ time git status
# On branch master
nothing to commit (working directory clean)

real    0m0.691s
user    0m0.256s
sys     0m0.356s

$ cd ..
$ rsync -a kernel/ kernel2/
$ cd kernel2
$ time git status # several times!
...
$ time git status
# On branch master
nothing to commit (working directory clean)

real    0m2.705s
user    0m1.724s
sys     0m0.816s

$ git reset
$ time git status
# On branch master
nothing to commit (working directory clean)

real    0m0.704s
user    0m0.296s
sys     0m0.348s

Regards,
 Andreas.