Or might this be related to pump.io#1216? Tried this with a non-broken account and got the same thing:

https://archive.is/QSBal

Further detail:

After following with AS, I followed with the Web UI (not visible to the public). It did not detect that I was already following. I did some tests and unfollowed/followed again from Web UI.

When I then unfollowed/followed with AndStatus (visible in the capture above, in this comment), it created the expected activities.

@clacke Thank you for noticing. Following your report I took time to find out, whose messages in Pump.io and why I get in my timeline.
This looks like there was some bug/data failure in Pump.io, but currently I was able to follow/unfollow Pump.io users via AndStatus. And as you noted, in order to fix my follows I had to:

1. "Follow" via Web Pump.io interface a person, whose messages I received constantly (without following...).
2. Unfollow then follow again people, who were marked as Followed by me, but whose messages I didn't receive for a long time.

I see via Web interface: "AndStatus@Identi.ca followed EVAnaRkISTO"

After this I saw him as "following by andstatus@identi.ca" in AndStatus and could "Unfollow".

I see via Web interface: "AndStatus@Identi.ca stopped following EVAnaRkISTO"

Then I successfully Followed another user via AndStatus:

I see via Web interface: "AndStatus@Identi.ca followed JanKusanagi"

Then I went to a list of people, whom I follow: https://identi.ca/andstatus/following - I fould out that I didn't receive their messages for a long time. I unfollowed/followed them again via web interface...

There is definitely something wrong with Pump.io: At identi.ca I see that now I follow sazius@pump.saz.im, but when I go to his site: https://pump.saz.im/sazius and Log in there, I still see "Follow" button, as if I don't follow him. Pressing that button gives some "Internal error"...

I'd like to point out that I've never seen this type of "broken activities" created by any other client.
The closest thing would be a "JaneDoe followed a person", which happens when trying to follow a wrong ID, such as "invented-does-not-exist@nonexistantserver.lalala". That's easy to reproduce.

@clacke, could we know who you were trying to follow when those activities were created?

@yvolk, is there a way he could get the JSON sent by AndStatus when those activities happen?

@jankusanagi I couldn't reproduce such erroneous activities that @clacke noticed: as I wrote above, all Follow/Unfollow activities, sent by AndStatus, looked normally via web UI at identi.ca

As the activities only say "Followed unknown xyz" I actually don't know whom I was trying to follow. And my .../following is broken as seen in pump-io/pump.io#1216, so I can't check. :-/

I will try and see if maybe I was following some recent followers back.