gnucash requires the libpopt.so library yet doesn't include it as a dependency in the ebuild. I somehow unmerged popt and gnucash stopped working. However, re-emerging gnucash did not fix the problem because popt wasn't listed as a dependency.
added popt dep to current stable (1.6.8) and current latest unstable (1.8.3) ebuilds, that should take care of it. Thanks for your report.