I agree that the response you received from L-Soft support is unacceptable.
But I also think that the person who answered you genuinely misunderstood
the issue, because we do have a fix that should address your problem:

144-0003 05/07/12 [B] Incorrect boundary used in generated bounces

Or rather, this is *my* determination based on reading your problem
description. You could of course have a different problem with the same
symptoms. But the fact that people with August 2005 builds cannot reproduce
the problem suggests that it is in fact the fix you need.

  Eric