DTPO 2.9 sync transfers indexed Dropbox folder over and over

After I posted my question I did stumble over another user with the same problem:

I should note (in answer to questions made to him in that thread) that:

  1. I did not use the sync beta software – my syncstore was created in the released 2.9 version,

and

  1. For some reason, nothing happens when I choose the “Report Bug” function in DTOP. If this is supposed to generate an email, I should note that I do not use Apple Mail (PostBox is the default mail client on my system).