I just noticed that I can access items both with & without the category in the URL.
When accessed without the category in the URL, the main menu does not show it's current location, but the breadcrumbs does contain the category.

Note: SEF enabled

Why is this happening? How do I stop access to the item "without" the category in the URL?

Hello Joe,

K2's URLs work according to Joomla!'s standards.
You can do the following to override this.
a) Use K2's advanced SEF (K2 Advanced settings) or
b) Use an SEO extension that supports K2, like sh404sef

I am using the K2 SEF parameter, I do not want to use an additional SEF extension.

This is the results I am receiving:

SEF Enabled ---

domain.com/category1/sample-item > page renders (this is the correct URL)
domain.com/sample-item > "category" removed still renders page (bad thing)

SEF Disabled ---

domain.com/category1/item/428-sample-item > page renders (this is the correct URL)
domain.com/category1/428-sample-item > "item" removed, redirect to category1 page
domain.com/item/428-sample-item > displays page (bad thing)
domain.com/428-sample-item > produces 404 Error

Overall, what I'm saying is that the removal of the category from the URL does not normally produce the page, it should instead redirect to the user to the homepage and not still display the item outside of the category.

Here is an example of how it should behave without the category in the URL (a site I found in this forum)

luxehighlife.com/jewellery/sotheby-s-hong-kong-to-auction-off-over-90-million-worth-of-jewels (with category: renders page)
luxehighlife.com/sotheby-s-hong-kong-to-auction-off-over-90-million-worth-of-jewels (withOUT category: renders HOMEepage)

Hello Joe,

You can redirect all 404 errors to your homepage either in your template or from your .htaccess file.
stackoverflow.com/questions/2363520/redirecting-404-error-with-htaccess

As for the links to links to the item. WIthout an SEO extension you need to create a rule that requests starting with /item/ should be redirected to the item page.

Thank you for responding. I think I may have figured out what was happening. I believe the issue is being caused by an extension. I am still resolving the issue, but at least I am in the right direction, where as before I was in the dark.

Thank you for the continued K2 Support :)

You 're welcome Joe.
Let me know of the outcome.