Please bump libwacom to version 0.8. Reproducible: Always
Since the latest version in portage (0.7.1) is over a year old and does not support the 3.17 kernel, this is now quite an urgent bug, since it causes unexpected breakages because settings are not appropriately set when upgrading to the latest kernel.
+*libwacom-0.10 (25 Oct 2014) + + 25 Oct 2014; Pacho Ramos <pacho@gentoo.org> +libwacom-0.10.ebuild, + -files/libwacom-0.5-eraser-bamboo.patch, -files/libwacom-0.5-eraser.patch, + -libwacom-0.5.ebuild, -libwacom-0.6.ebuild, -libwacom-0.7.ebuild: + Version bump, drop old +