The API documentation for this method states that it

Determines all the IP addresses of a host, given the host's name. The host name can either be a machine name, such as "java.sun.com", or a
string representing its IP address, such as "206.26.48.100".

However, if an IP address is passed as a parameter, the only IP address that is
returned is the address itself. This can be seen from the source in InetAddress.java:

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    public static InetAddress getAllByName(String host)[]
    throws UnknownHostException {

    if (host == null || host.length() == 0) {
        throw new UnknownHostException("empty string");
    }

    if(Character.isDigit(host.charAt(0))) {
        InetAddress[] ret = new InetAddress[1];
        ret[0] = getByName(host);
        return ret;
    } else {
        return getAllByName0(host);
    }
    }

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This bug should not be confused with 4026796, which reported a separate problem.