I can confirm this error. I have been getting it after some recent updates. Newer Mylivecd and drakxtools packages have been hitting the repo. I install and remaster, but the same error exists when trying to partition. Even "Use existing partitions" gives the error.
Workaround for time being: use gparted (or another partioning tool) to create the partitions, then in live installlation choose "custom disk partitiong", just keep the existing partitions and click next, it will skip over the partitioning bug and install successfully.
I'm glad it wasn't something I've done wrong, hopefully it will get fixed soon.