libplasmaclock-4.8.0 specifies OPENGL_REQUIRED="optional", however the ebuild does not control WITH_OPENGL in any way, and I cannot locate any evidence that it actually makes use of opengl.
This is true, unfortunately OpenGL is still required because of silly workspace-global OpenGL check (which should be done only for kwin).
(In reply to comment #1) > This is true, unfortunately OpenGL is still required because of silly > workspace-global OpenGL check (which should be done only for kwin). Does it matter, if the installed files do not change? Some other packages from kde-workspace (eg. kmenuedit) do not reference opengl in the ebuild.
Fixed. Thanks for reporting.