My best friend and I used to get so many either ninja kin invites or people pestering us through tells about it that we eventually went and used all of our alts to make a Kin of our own. Seems like having a Kin name floating under our usernames did the trick, since once an alt joined our kin, the pestering stopped.
As for any rhyme or reason to it.... I've actually noticed that it happens more on my low-level toons that start in or near the Bree-land area, I don't ever remember this happening in the Ered Luin area, or in places farther away from Bree.
What I have had happen a LOT is a very similar thing with fellowship invites- usually along the lines of me being in a high-level zone, and all of a sudden some low-level toon back in Bree will start spamming me with Fellowship invites, and never respond when I PM them asking why they want my help. And they usually don't stop until I have either added them to ignore or I've logged off and switched to another toon.
[COLOR="#8B4513"][MY ALTS] [B]Balvur[/B] warden/ [b]Hallti[/b] guardian/ [b]Hila[/b] burglar/ [b]Elenauriel[/b] runekeeper/ [b]Dolmifaynar[/b] minstrel [/COLOR]
I speak my mind because it [COLOR="#B22222"][i]hurts[/i][/COLOR] to bite my tongue