The MACHINE should be saved with ?=, because if it is saved using = it can not be overwritten from command line using MACHINE=x bitbake core-image-.. ALso, the comment #added by bitbake, should be replaced with #added by hob, to reflect the reality.
patch sent on bitbake-devel.
patch merged: http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=45392cc67a89afe468b179789c7fbeeb3aa67769