Getting mixed themes when user is not logged in and using AJAX form.

Thank you for your quick reply.

Are you using the AJAX functionality the drupal core provides or did you implement something by yourself?
I am using Drupals built in AJAX functionality by simply specifying the #ajax parameter on my submit button and nothing more.

$form['submit'] = array(
  '#type' => 'submit',
  '#value' => t('Submit'),
  '#attributes' => array('class' => array('submit')),
  '#ajax' => array(
    'callback' => '_display_form',
    'wrapper' => 'ajax_wrapper',
    'effect' => 'fade',
    'event' => 'click',
  ),
);

Did you configure /admin/config/user-interface/themekey/settings/ajax?
I noticed in the docs that it mentioned something about some AJAX settings, but I do not see them anywhere in my ThemeKey settings. I looked everywhere. I went to the above URL you provided and I do not see any AJAX settings. I took a screenshot and attached it to this post for you to see what I get when I go to that URL you provided.

Do you use method POST when submitting the form using AJAX?
I am using what Drupal uses by default when specifying the #ajax parameter on a submit button, which yes is POST.

Does your POST contain $_POST['ajax_page_state']['theme'] and $_POST['ajax_page_state']['theme_token']?
I'm not sure how to verify this. I am not specifying these things in my code anywhere. Should I be? If so, I'm not sure how. Since this is an AJAX submit, I'm not sure how to verify those values exist upon post.

Thank you for your help!

Sweet, that's what I was actually going to try next anyway. I'll update and report back. THANKS!!

Arg. So it's still not working after the update. I even tried disabling and uninstalling and then re installing v3.0 and reapplying my rule chain (and clearing cache), but when a user is not logged in, they get the mixed theme after AJAX submit. I uploaded a screenshot of what my AJAX settings are set to.

Still happening with the Bypass option checked and all themes set to safe. :-/

So I decided to try something. I completely disabled ThemeKey and added the following code to my custom module:

function job_agent_custom_theme() {
  if (arg(0) == 'vista') {
    return 'vista';
  }
}

This did exactly what I was trying to accomplish with ThemeKey and switched my theme to a custom theme based on the URL. The funny thing is I have the EXACT same problem I had with ThemeKey and ThemeKey is completely disabled, so it's not a ThemeKey issue, but a Drupal issue. I'm still in the same boat though and don't know how to fix it, but thought that was interesting.

Whats the best way to dump those variables? Since it is an AJAX post when I do a print_r($_POST) in my form submit method, I just get a JavaScript alert box that has a TON of variables in it so much so that it goes off the bottom of the screen and there is no way to read it all because there is no way to scroll the alert box.

Or I can dump specific variables then if you want to make it shorter and more readable. ??

Also for the other questions:

The destination URL is the same as the original form. The submit is just posting to the same form and I am then modifying the form that gets rebuilt filling in data from the database based on the email address.

And my ThemeKey rule is very basic. I actually only have one for this specific need and it is :

drupal:path = vista/job-alerts which will change the theme to "vista"

SWEET! I installed the themekey-7.x-3.x-dev version and it fixed the issue! Thanks so much for taking the time to look at this. Much appreciated.