Here's a problem that I've been fighting a loosing battle with: Proper validation with W3C.
I think the problem lies with WordPress removing spaces in the attributes within tags. Here's the page in question: http://www.lagrecaarts.com/shop. When looking at the page in code view, everything looks good. But the code output view in the W3.org page clearly shows the spacing missing between the href and title attributes.
I've switched themes to test, no change.
I've turned off the "correct invalid nested XHTML.." option, no change.
And funny, but there doesn't seem to be a problem with my homepage, which also has hyperlinks.
Any ideas, other than "disable the visual editor"?