socket ID returned from socket(AF_INET, ....) in ESP32 does not start at 0

On ESP32 call of socket(AF_INET,.....) returns a socket ID + an offset(named LWIP_SOCKET_OFFSET)
This results in an error message during check of socket against maxsize (32)

Is there any limitation inside Espruino for socket ID, except this assert, for range of sockets ?
With other words, is this socket ID used somewhere in Espruino, for example as a pointer to an array ?