A few days ago I read Deane Barker's excellent post Editors Live in the Holes (go ahead and read the post and then come back) and I have been thinking about it ever since. I have had the same experience several times and it is a good reminder for developers to pay special attention to configuring and testing the rich text editor. As Deane points out, it is too easy for developers to disregard "the holes" as a contributor problem, not a system problem.
To get it right, the holes need to be jointly owned by the designers, developers, and content contributors. Designers need to design for flexibility. Developers need to do everything they can to make contributors successful. But this raises something of a chicken and egg problem — at least for new CMS implementations (as opposed to migrations). In these projects, content entry typically occurs after the system is considered complete. This means that the designer and developer need to anticipate what rich text capabilities (formatting controls and the styles that control the display of rich text) the contributors will need. This is particularly important in the ever-present "generic page" content type that is typically used for the many one-off (odd ball) pages that exist in any website.
I have found two good techniques to get around this problem. First, it is good to test the rich text editor with a few of the more challenging one-off pages on the site. Take a page with embedded images and objects (like perhaps a Google map) and formatting and try to reproduce it in the rich text editor. Don't disable the rich text editor and edit the source. That is cheating. If it turns out you can't do it without pulling your hair out, you need to come up with a work around. If it is a really important page, you might need to develop a special content type and/or presentation template that does some of the work. If you find that there are too many challenging one-off pages to choose from, you might step back and consider enforcing more uniformity between pages. Otherwise, you will probably not be getting all of the value (content reuse and manageability) out of a CMS.
The second technique is to build a "style guide" page and place it in some discrete area on the site. The style guide page is a generic page that contains examples of all the stylings that are available to the contributor. For example, every heading level, paragraphs, lists (ordered and unordered), tables, embedded images, etc. The content contributor can visit this page to get an idea of what is possible and then open it in edit mode to see how the formatting was executed. The process of building and reviewing the style guide page is a useful forum to get designers, developers, and contributors together to collaborate and align. The fact that it is so tangible grounds everyone in the real capabilities of the platform. The style guide page is also the first place to check updates or enhancements to styles after launch.
At the end of the day, designers, developers, and contributors all want the site to be a success. They can't just claim victory on their little piece ("the mockups were approved," "we got out of QA," or "I got my page to preview!"). Editors may live in the holes but everyone has to keep the holes clean.