https://bugzilla.redhat.com/show_bug.cgi?id=845956
--- Comment #18 from fujiwara tfujiwar@redhat.com --- Recently I added a dconf key switcher-delay-time: https://github.com/ibus/ibus/commit/dce22003c388a7274dc148161cf0e02f44d29ad6
If the key switcher-delay-time < 0, the IME switcher window is not shown and switches the first two engines only with Ctrl+space and Ctrl+Shift+space. So I guess your problem might be resolved here without Ctrl+Shift+space customization through VM box problem still exists.