Qt/5.8, XCB/Unity: Application startup crash in Gtk3 platform theme

Opening creator/assistant/designer still fails with #519 No xcb issues anymore, just

~/Qt5.8.0-beta_519/Tools/QtCreator/bin$ ./qtcreator
qt.network.ssl: QSslSocket: cannot resolve SSLv2_client_method
qt.network.ssl: QSslSocket: cannot resolve SSLv2_server_method
Segmentation fault (core dumped)

and

~/Qt5.8.0-beta_519/5.8/gcc_64/bin$ assistant
assistant: could not exec '/usr/lib/x86_64-linux-gnu/qt4/bin/assistant': No such file or directory
jaheikki3@jaheikki3-ThinkCentre-M93p:~/Qt5.8.0-beta_519/5.8/gcc_64/bin$ ./assistant
Segmentation fault (core dumped)