FreeBSD-10.3-RELEASE-i386-memstick.img installer changes contents of USB flash drive?

[David Christensen]

freebsd-questions:

Using Debian GNU/Linux 7.11, I downloaded
FreeBSD-10.3-RELEASE-i386-memstick.img and burned it to a USB flash drive:

        # time dd if=FreeBSD-10.3-RELEASE-i386-memstick.img of=/dev/sdc
bs=1M conv=sync; sync
        659+1 records in
        660+0 records out
        692060160 bytes (692 MB) copied, 141.567 s, 4.9 MB/s

        real    2m21.571s
        user    0m0.004s
        sys     0m1.696s


If I compute the checksum immediately after burning, it matches the
published checksum:

        # time dd if=/dev/sdc count=1350917 | sha256sum -b
        ab104a30627754bb8d39eeff3c5c5a4a15537d32c749e2b9841b34cb08e17eb0 *-
        1350917+0 records in
        1350917+0 records out
        691669504 bytes (692 MB) copied, 43.252 s, 16.0 MB/s

        real    0m43.257s
        user    0m7.236s
        sys     0m3.496s

        # grep
ab104a30627754bb8d39eeff3c5c5a4a15537d32c749e2b9841b34cb08e17eb0
CHECKSUM.SHA256-FreeBSD-10.3-RELEASE-i386
        SHA256 (FreeBSD-10.3-RELEASE-i386-memstick.img) =
ab104a30627754bb8d39eeff3c5c5a4a15537d32c749e2b9841b34cb08e17eb0


But after using the USB flash drive to install FreeBSD, the checksum has
changed:

        # dd if=/dev/sdc count=1350917 | sha256sum -b
        1350917+0 records in
        1350917+0 records out
        bd159b85486322febe992226bbec9c86d96d70dd1e5a8b7c6f0bb9d29eb50df3 *-
        691669504 bytes (692 MB) copied, 42.989 s, 16.1 MB/s


Therefore, the FreeBSD-10.3-RELEASE-i386-memstick.img installer has
changed the contents of the USB flash drive.


Why?


David