www-plugins/lightspark-0.4.3 currently has an automatic dependency on gnash (search CMakeLists.txt for GNASH_EXE_PATH). While the default path set by upstream matches the path gnash is installed to by Gentoo, the possible dependency of lightspark on gnash should probably be documented via a useflag. Reproducible: Always
It only sets the location of the "gnash" executable based on what it detects, and falls back to /usr/bin/gnash if it is not found. Coincidentally, /usr/bin/gnash is where Gnash is installed on Gentoo, so the result is the same no matter whether Gnash is installed or not.
Resolving as WONTFIX.