I noticed this in the case of webkit-gtk (in a personal overlay, but that shouldn't matter), which DEPENDs on rubygems, which in turn has a recursive RDEPENDency on dev-lang/ruby. `emerge --depclean --with-bdeps=y` would not clean any of the ruby packages unless webkit-gtk was fully deselected. I suspect it did not detect the recursive dependency. I attach the ebuild of the overlay (I just use it to pull in the dependencies) for review, just in case.
Created attachment 516992 [details] webkit-gtk ebuild causing the dependency
If you want to remove DEPEND packages, you need to use --with-bdeps=n instead.
Thank you and apologies for the false bug.