If I remember correctly, then bindings read the state of the binding point when trying to use them as toggle. I know there is a thread somewhere about it, but I can’t figure out what to search for.
Anyway, my suggestion would be to try to use a binding to connect to the value you want to toggle and see if you can toggle it that way. I’ll see if I can find the thread, though.
Edit, found it: Feature Request: "toggle" binding for VST parameters