Scanning the logs, it looks like all of the returned tweets have a twitter short url at the end.
The plot thickens. In a sample of a few dozen tweets they all have the same expanded url:
I don’t see anything in the url or the tweet that should be triggering our filter.
OK, I think I’ve narrowed it down. We are using the hashtag “@twitter” as sort of a “keep alive” signal, because when we’ve tried to restart a hosebird client it won’t respond until a new tweet comes in. So filtering on @twitter gives enough traffic that the client restart is responsive.
The extra tweets we’ve been receiving have a tweet link in them, and that tweet has a @twitter mention. We filter out tweets with @twitter in the text or in the list of hashtags, but have not tried to filter out tweets that are linking to other tweets with an @twitter mention.