Umm, numeric 442 has nothing to do with /invite. /invite may use it, but you can NOT assume that is all it is used for.
According to RFC1459:
"<channel> :You're not on that channel"
- Returned by the server whenever a client tries to
perform a channel effecting command for which the
client isn't a member.
Therefore, how should mIRC know you invited someone when you aren't on the channel? mIRC doesn't know what command made the server generate that response, only you do.