Kickstart is changing order of partitions when they are created

Issue

When using the following kickstart configuration on RHEL 6.2, the ordering of the created partitions are the same as in the kickstart configuration.

clearpart --all --drives=${GRUBDEV} --initlabel

part /  --fstype=ext2 --fsoptions="" --size=1650 --asprimary --ondisk ${GRUBDEV}
part /flash  --fstype=ext2 --fsoptions="" --size=2048 --asprimary --ondisk ${GRBDEV}
part /servpart  --fstype=vfat --fsoptions="" --size=100     --asprimary --ondisk ${GRUBDEV}

When using the same kickstart configuration on RHEL 6.3 the ordering of the created partitions is not the same as in the configuration file. On RHEL 6.2 the root partition was always created as sda1, on RHEL 6.3 it is now sda2.

How can we guarantee that the root partition is always sda1?