At parse time INCOMPATIBLE_LICENSE checks LICENSE and if the LICENSE is on the list of INCOMPATIBLE_LICENSE then the entire recipe is excluded. In some circumstances, given a recipe with: LICENSE = "GPLv2 & GPLv3" LICENSE_${PN}-foo = "GPLv2" LICENSE_${PN}-bar = "GPLv3" package foo, while GPLv2 will be skipped, even though it is not incompatible.
This was fixed at: http://git.yoctoproject.org/cgit/cgit.cgi/poky-contrib/commit/?h=eflanagan/incompatible_license&id=a455f24986a67550a5495cc77d7073e044c7499f