I've encountered the same problem with the openafs-kmod package.  The only solution I've found was to have a 

BuildRequires: kernel-devel = %{kver}

... because the kernel-debug-devel provides "kernel-devel = 3.10.0-123.13.2.el7.debug"

This is why it finds it when you don't specify the kversion.  Red Hat, in their infinite wisdom, made the kernel-debug-devel provide kernel-devel, and the RPM sorting algorithm finds that "3.10.0-123.13.2.el7.debug" is a later version-release than "3.10.0-123.13.2.el7".

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