Edit, 2 April 2016, Torsten
The bug seems to be fixed by rjsmelo r58016 - ( thx Nelson for emailing me).
Before I close, I want to do a more in-depth test later to night or so, but it really seems to work (did resend out a wikisyntax-wysiwyg html+ txt version newsletter, that previously caused false encoding when received and today it was sent and received smoothly and intact).
Before I describe in detail, I`ll setup a show instance.
To help developers solve the bug, we kindly request that you demonstrate your bug on a show2.tiki.org instance. To start, simply select a version and click on "Create show2.tiki.org instance". Once the instance is ready (in a minute or two), as indicated in the status window below, you can then access that instance, login (the initial admin username/password is "admin") and configure the Tiki to demonstrate your bug. Priority will be given to bugs that have been demonstrated on show2.tiki.org.
Unable to connect to show.tikiwiki.org. Please let us know of the problem so that we can do something about it. Thanks.