Fundamentally, though, how can it be stopped? The two instance administrators can only see part of what's happening, and can't directly determine that the votes are coming from two alts of the same user. Maybe over enough times, the patterns can be guessed at with heuristics, but this kind of vote manipulation is going to be a problem for federated communities. Especially if we don't get better moderation tools developed.
vote manipulation is going to be a problem for federated communities
I guess, but since the feed isn't algorithmically created to maximize engagement (the tools are better than commercially driven sites) I don't think it matters as much. I think of it as a "Who's Line Is It Anyway" condition - everything is made up and the points don't matter. And, tbh, I really like that I can click into a stupid-x story without worrying that I'll be fed stupid-x content for the next week. It's worth a little vote tomfoolery, imho.
I'll do this if it's important information that needs to be shared and seen by more people. Otherwise I don't bother. I'm not in it for the doots. I'm here for the community.