Below is a post I put on the site where I got the package.  One of the developers there suggested I post here to see if more specific information can get out for everybody.

My question is that when a site has K2 and the new users(even - SuperAdministrators) are created they do not show in the Joomla user manager, where do they go, and how can this be put back to normal upon uninstall of K2?

I actually did try to recreate this problem without the quickstart and I got same thing.  New users created after uninstall of K2 do not show in Joomla User manager.

Thank you so much for your help.  Unfortunately I could not wait, and I had to reinstall the site and use the Joomlart template without the quickstart.  

I will try this next time, tho, I really love T3 templates and I'm sure I will need this in future.

In terms of extension enhancement which is done through template override through::

template/ja_portfolio/html/com_k2

You could have simply renamed the specific folder and override wont apply then. The extension functionality and styling would return to default stage which is powered by the extension files