ibus switching between input methods no longer working on 16.04

Just ran into this hiccup when upgrading, and input methods always give me hell whenever I upgrade my distribution, so I thought I'd post the answer here.

Go into the preferences interface window (via preferences on the panel menu, or alternatively by right clicking the panel icon), navigate to the advanced tab, and then uncheck "use system keyboard layout". This will stop your default system layout overriding ibus when you toggle between layouts.

I found that ~/.config/ibus/bus owned by root and user can't access it. There should be IBUS_DEMON_PID maintained by daemon. So change the owner and restart PC to populate the relationship. That helped me