It only can be set to "True", which is not common in oe, e.g.: QEMU_USE_KVM = "True" # works QEMU_USE_KVM = "1" # Nothing, does't work, this would surprise the user. We can make it work with both 1 and True.
I concur, it is an easy fix. I also got burned by the assumption "1" would work ....
http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=60ceabb92276ff182042c866b3e6e25fe9ff20d1