I'm not sure where they slipped in, but custom partition tables are ending up with DOS style line endings. This causes kickstart to fail miserably, since this command:

echo foo > /tmp/diskpart.cfg

ends up becoming:

echo foo > /tmp/diskpart.cfg\r

which creates diskpart.cfg\r instead of diskpart.cfg. I couldn't figure out where in the path they're appearing (web browser, rails, mysql, etc), but I did a simple patch to filter them out of the generated kickstart script.