Fresh version Debian 9.4 Stretch, bug is still here. Workaround: Unpack .deb of gir1.2-ibus-1.0, replace "gir1.2-ibus-1.0" to "gir1.2-ibus-1.0:i386" (or :amd64 or whatever) inside DEBIAN/postinst and DEBIAN/prerm, re-create .deb file again, install it via dpkg. Done.
-- Roman
