When using the fop2 manager, you can create groups and then assign groups to a user to limit what he can view. As those created groups contain only local buttons, if you select groups for any given user, then any remote or custom/manual buttons you might have added won't appear. So, if you add remote buttons while manteining the fop2 manager autoconfiguration, you must not select any groups for any user, as it will be limiting those custom buttons from view.
You can add custom buttons while still using manager configuration by adding things to:
/usr/local/fop2/buttons_custom.cfg
But remember NOT to use groups (do not select any groups on the user tab in the manager).