If what you're experiencing is what I think it is, then it's this Pump.io issue. Mentioned in the BUGS file, btw =)

In that case, don't worry, you're only flooding yourself. That kind of duplication isn't real.

In my experience, the most common case is:

• You post a comment to your own post.
• You see your "posted a comment" activity twice.
• If that's the last you got in the Meanwhile feed, and update it again, the server will send that activity to you again. If you update again, it will send it once again, one each time. The cycle is broken when there's a different activity in the feed, maybe you liked something else, commented on something else, or somebody else did something.

You can verify if this is your case by closing Dianara and starting it again. Your Meanwhile feed should show your "posted a comment" twice, at most.