inet_ntoa() returns 1 (success) when called with a parameter that is just the initial part of an IP number. For instance, it claims to correctly convert each of "129.79.", "129.79", and "1". I don't know whether this is the BSD behavior, or whether it is intended, but it at least doesn't seem to be consistent with the manual, which specifies that the argument is an Internet host address in "standard numbers-and-dots notation."
The standard does not specify it actually, this behaviour matches BIND and Solaris behaviour. E.g. Irix accepts a trailing dot as well.