The slot is not specified. This causes kde-base/kdepimlibs:4 to suffice. I guess this is an eclass problem. Anything with SLOT 5 should get SLOT 5 for dependencies created by eclass functions. Reproducible: Always
Thanks, fixed in git. https://github.com/gentoo/kde/commit/3c454f1fab9e64285b751039a4b4d4801095bb3a