Hi Dave,
You can submit a bug at codeplex.com/umbraco/
However, this is a known problem, as the validator is a standard .NET validator. It does not work correctly with a few type of controls such as the Checkbox list, Radio Button List, Upload, and possibly a few others.
There was a short discussion with the core developers about making modifications to the controls that would allow for custom validators such as a checkbox validator, but, I don't believe it is planned for release until version 4, which is ways off.
You can create a custom version of the editor control which will handle validation itself relatively easily.
Case
• 2007/2008 MVP • 2008/2009 MVP • Core Developer • Certified Professional Level I & II •