checksum/disk theories?

[Tom Horsley]

I have the f12 Beta dvd images run through "split -b 1G" on
a vfat usb stick. For both the i36 and the x86_64 images
when I do something like this:

cat Fedora-12-Beta-x86_64-DVD.isoa* > ~/Fedora-12-Beta-x86_64-DVD.iso

The sha256sum -c fails on the resulting file :-(. (The checksums
checked OK on the original files I downloaded).

Then I do this:

cat Fedora-12-Beta-x86_64-DVD.isoaa > ~/Fedora-12-Beta-x86_64-DVD.iso
cat Fedora-12-Beta-x86_64-DVD.isoab >> ~/Fedora-12-Beta-x86_64-DVD.iso
cat Fedora-12-Beta-x86_64-DVD.isoac >> ~/Fedora-12-Beta-x86_64-DVD.iso
cat Fedora-12-Beta-x86_64-DVD.isoad >> ~/Fedora-12-Beta-x86_64-DVD.iso

The resulting file is the same size as the one I got the 1st time,
but this file passes the sha256sum -c.

Has bash started randomly ordering wildcard expansion or something?

Has my usb stick flaked out and only works right when I read the
same set of files twice in a row?

I got the exact same results getting the i386 images off the usb stick
as well.

What is going on?