Hm well reason we always first do upgrade before dist-upgrade is that we've experienced several times over time that a node would get a NMI fired as SW watchdog sometimes was held down for longer than 60 sec by some package patching taking too long time, like grub probing our iSCSI luns/LVMs on iSCSI. Hence we've postponed kernel and thus grub patching to a dist-upgrade after most other package patching has been performed in an regular upgrade. Even as suggested w/dpkg --purge os-prober, grub patching is still is too slow ImHO.