ibus not appearing in StatusNotifierItem spec-compliant system tray

This one is tricky as I have heavily customized my setup, but it has been bothering me a lot so I decided to ask a question. Recently, ibus stopped appearing on the system tray. While my system tray is not the typical one people use, it does comply to the freedesktop's StatusNotifierItem specification. I don't think a program as famous as ibus would have status notifier not compliant to the standard. Do you have any clue what is happening? Which system diagnostics could I dig up to pinpoint the problem? Any direction (excluding "use another system tray") would be appreciated! EDIT: The option "Show icon on system tray" is definitely turned on.