You're getting this bug because the package in summary installs its documentation (or at least part of it) outside the usual /usr/share/doc/${PF} directory. First, please keep in mind that this bug might not be noticeable for -r0 ebuilds, but it might be for -r1 and later, since if the ebuild has same name and version of the package, for -r0 it might correspond properly. To fix this, if the package uses autotools, recent version (autoconf 2.61+) have two ./configure switches: --docdir and%2
Fixed with revbump.