Please bump to 0.28.1 which got released on 17 February 2017: http://gparted.sourceforge.net/news.php?item=208
Created attachment 471892 [details, diff] gparted-kdesu-integration.diff I don't have an ebuild, but a suggestion for changing back kdesu integration for the bump.
Fixed in commit https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=61449f219b9599be354d7ce6d88690c9ce7f91bb. Thanks for reporting.