Please update mousepad ebuild. http://git.xfce.org/apps/mousepad/tag/?id=mousepad-0.4.0
+*mousepad-0.4.0 (09 Mar 2015) + + 09 Mar 2015; Michał Górny <mgorny@gentoo.org> +mousepad-0.4.0.ebuild, + metadata.xml: + Version bump. Upstream added optional GTK+3 support, started using GSettings + and improved GUI configurability.