Code messed up and image attachment missing from second and subsequent emails

Hi, I have installed latest official release of simplenews (6.x-1.0-rc6). I am using D6.
I have also installed the latest mimemail (6.x-1.0-alpha1) in order to send out HTML emails.
I have also the PHPmailer module active.

Everything works fine, but for a strange bug.

It looks like that the newsletter email is sent out OK to the first recipient of the list, while the subsequent are NOT OK.

This happens for Test emails as well as for actual newsletter subscribers.

I shuffled the recipient list and can confirm the first one receives the email OK, independently of the mail address and client (tested with thunderbird, webmail) etc.

Resuming:
I compose a HTML newsletters using FCKEDITOR.
I add one image to the newsletter (not as attachment, but into the HTML code, as tag).
I send the newsletter (either to test addresses or to subscribers).
Only the first recipient will see the image in the newsletter (and it is correctly sent out as attachment to the newsletter).
The following recipients receive a sligthly different email, that is:
*** it comes without the image attached
*** the text version is not separated but is inline with the HTML version.

Can anybody else confirm the issue?