setting a wrong IP address in multiplayer mode (host) leads to the known error message "bind failed", of course.
What I wonder is why this also applies to the insim port? So if there is a wrong IP address setting, LFS is not able to initialize the insim port too.
Maybe it is not really a bug but more a kind of GUI design decision to devide the setting into 2 settings, because insim and host are 2 different servers running in LFS and not related to each other.

There are two possible ports. One for the gamers and the other for InSim. InSim takes the same IP as the host, so there is only one IP bind error to be had. The host config option "/insim=" is a config allowing incoming/outgoing connections to external inSim programs/scripts. It is not an error if there is no inSim app or script present to connect with it. You would get an error at the application end, rather than the LFS dedicated host end, if there was a problem establishing a connection with the host.

Hope that explains it