Compilation of the accessibility plugin is commented out in the qt-gui-5.0.0 ebuild. It seems like without this plugin all widget based application crash if there is no accessibility D-Bus agent avaliable. However, when I enabled compilation of the plugin (BTW, I did not see sandbox violation), widget based application (designer and assistant) started to work fine. Interaction with menu does not produce crashes anymore. Reproducible: Always
Yeah, the sandbox violation (reason why I disabled the plugin) was fixed as a side effect of commit 8c39b4c05fecf1e0c1713c19b5e077c47e881846 in qtbase, but I didn't notice. The plugin is now re-enabled, thanks for reporting.