Magento2 – pub/static Loading Only via HTTP

There is a function just for that, called shouldUrlBeSecure located in app/code/core/Mage/Core/Model/Config.php on line 1477.

Here is the complete function:

/**
 * Check whether given path should be secure according to configuration security requirements for URL
 * "Secure" should not be confused with https protocol, it is about web/secure/*_url settings usage only
 *
 * @param string $url
 * @return bool
 */
public function shouldUrlBeSecure($url)
{
    if (!Mage::getStoreConfigFlag(Mage_Core_Model_Store::XML_PATH_SECURE_IN_FRONTEND)) {
        return false;
    }

    if (!isset($this->_secureUrlCache[$url])) {
        $this->_secureUrlCache[$url] = false;
        $secureUrls = $this->getNode('frontend/secure_url');
        foreach ($secureUrls->children() as $match) {
            if (strpos($url, (string)$match) === 0) {
                $this->_secureUrlCache[$url] = true;
                break;
            }
        }
    }

    return $this->_secureUrlCache[$url];
}

To see which URLs should be secure you can add a simple Mage::log($secureUrls) inside the if statement. This is what my log entry looked like:

2014-02-12T11:55:26+00:00 DEBUG (7): Mage_Core_Model_Config_Element Object
(
    [install] => /install/wizard/checkSecureHost
    [customer] => /customer/
    [sales] => /sales/
    [authorizenet_paygate] => /paygate/authorizenet_payment
    [checkout_onepage] => /checkout/onepage
    [checkout_multishipping] => /checkout/multishipping
    [paypal_express] => /paypal/express
    [paypal_standard] => /paypal/standard
    [paypal_express_callbackshippingoptions] => paypal/express/callbackshippingoptions
    [googlecheckout_redirect] => /googlecheckout/redirect/
    [googlecheckout_beacon] => /googlecheckout/api/beacon/
    [googlecheckout_api] => /googlecheckout/api/
    [review_customer] => /review/customer/
    [tag_customer] => /tag/customer/
    [wishlist] => /wishlist/
    [paypaluk_express] => /paypaluk/express
    [rss_catalog_review] => /rss/catalog/review
    [rss_order_new] => /rss/order/new
    [rss_catalog_notifystock] => /rss/catalog/notifystock
    [centinel] => /centinel/
    [newsletter_manage] => /newsletter/manage/
    [downloadable] => /downloadable/customer/
    [downloadable_download] => /downloadable/download/
    [ogone_api] => /ogone/api
    [persistent_onepage_register] => /persistent/index/saveMethod
    [checkout_cart] => /checkout/cart
    [storecredit_info] => /storecredit/info/
    [giftcard_customer] => /giftcard/customer/
    [enterprise_pbridge_pbridge] => /enterprise_pbridge/pbridge/
    [invitation] => /invitation/
)

Now to figure out how Magento switches HTTP to HTTPS I think you would most likely have dive into the Zend framework in the lib inside lib/Zend/Http/* because it contains files of most interest. Well, anyway hope this helped. Good luck!

One simple thing which could cause this problem is cache. First thing to try is to refresh and clear magento as well as browser cache.