Hello Artswhild -
I am sorry to hear about the difficulty you've run into on the preview page. I have tried, but was not able to reproduce an issue with the font change not appearing in Preview as you have described, so it is possible that it is specific to a certain template or there is another issue occurring for you that I am unable to reproduce within my account.
The second issue you describe is an issue that occurs with some customized templates after moving them into the new template system. Our engineers are aware of this issue and are looking into a resolution for it, and I will update this thread as soon as there is more information available regarding the old tags showing as text. However, you should be able to manually remove them from your template or from a saved or active listing as needed.
If you are using a custom template that may be related to the first issue as well. In order for us to look into that further, please file a support case from under the Help tab of the site that includes the details of what you've run into, which template you are using and the operating system and browser you use so we can look into that further.
- Craig