All qt 5 applications throw floating point exception due to zero division. See upstream bug report: https://bugreports.qt.io/browse/QTBUG-49322 and upstream patch: http://code.qt.io/cgit/qt/qtbase.git/patch/?id=79447068579ea93d616d840bb8cbbf8adb1ed6ec The patch should be added to qtgui-5.5.1 ebuild. Thanks to kensington for provided links.
Thanks, fixed in git. https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=293c6581f8173670b09ad92c903c4866565652a1