As I learned today there is already poky 1.5.2 which can be found on http://downloads.yoctoproject.org/releases/yocto/yocto-1.5.2/ Yet, the poky-dora file as well as the git HEAD of the dora branch (commit 19745990465b37107142c5464008ca9f7959cc0b) lists 1.5.1 in meta-yocto/conf/distro/poky.conf The documentation itself lists 1.5.2 in various files. Right now it is unclear to me if I hit the pre-release or if the DISTRO_VERSION was accidently not updated. If it is not a pre-release (shouldn't it be labled beta or similar?), I would suggest to update the tar.gz on http://downloads.yoctoproject.org/releases/yocto/yocto-1.5.2/ , too.
Fixed in the dora branch, thanks for reporting. We've also opened another bug to fix the release process so this doesn't happen again. http://git.yoctoproject.org/cgit.cgi/poky/commit/?h=dora&id=e6aafde7d201c714e2f9b88392b0d5efe53227d9