http://petesguide.com/WebStandards/entities/
I'm not sure if this is an issue that is caused by reliance on webkit, or if it is other parts of the Omniweb code. I checked this in safari, with similar errors presenting.
Presumably this guy knows what he's talking about (his site was linked from a 'list apart' article).
I'm posting this in case the site test results are correct and Omniweb / webkit is not fully HTML 4.01 compliant.