I could swear that you used to not be able to do this but... presently you can send a guild request to someone already in your gang. Not sure if this is a bug or not, but I can see no practicle use for this.

I'll check this.

I know that some guilds are quite dynamic, and even we tend to give people like King Pummel T an invite so he can return when needed.

I suppose it's a bug, but we've taken advantage of it.

EDIT:
I've checked. It doesn't even bother to check whether they are in you guild I must have wanted this functionality.
I should probably change it though.

I sorta know what you mean... leaving an open invitation and all. I just don't see the benefits in it since should said player ever leave a guild you can invite them then.