August 18th, 2015
If you're not familiar, there's a web page validation tool on the internet for free. It is called the "Markup Validation Service" and is provided by W3C. I've been using this for years, but for some reason have noticed an issue with it lately: when I try to validate by URI and have errors, when I fix them and try to re-validate, the tool doesn't grab the latest updates.
The issue appears to be that the site uses caching and that caused the validator to not see the latest updates. You may be able to verify that the site uses caching by using your browser's Network Web Developer Tool (if it has one) or by checking out the site's hosting provider's Web Cache Control Tool (if they have one).
To still validate your page without changing the cache settings, there is a work around.
Instead of using Validate by URI, use Validate by Direct Input. This is a little more work to copy all of the html code (and if you're using server side scripts, you'll have to view the page source and then copy and paste it into the area provided on the Validate by Direct Input page).
The only problem I see with this method is that you may be presented with the warning: "Using Direct Input mode: UTF-8 character encoding assumed" and the details that go with it. If you're concerned about this message, you can continue using the Direct Input tool to help you remove all the validation errors but then use the Validate by URI tool to make sure there are no encoding issues once you've finished removing every other error.