Hi Christian,
As Craig mentions, the editor we are using is called TinyMCE, which is a separate project in it's own right:
We included the code some time ago, so there may be some new bug fixes that we haven't yet integrated into Totara. I've created a bug to merge in the latest version, and hopefully that will fix the issues that you're seeing.
If not we'll take a look ourselves and try to get it working better.
Thanks for the examples of issues you are having, feel free to post anymore that you come across.
Simon