DeGeyter suggests that the problem typically arises when consumers enter secure mode by adding items to their shopping cart--and then continue browsing, viewing all ensuing content under the https: domain. The fix for this is simple.
"There is no reason to go secure just by adding products to a cart," he says. "The place to go secure is when they hit the checkout button." And if they leave the checkout process to continue shopping, they need to automatically be placed back onto non-secure pages.
"When shoppers can access secure and non secure versions of the same unsecure page, then likely the search engines can as well," deGeyter says. "This creates almost a complete duplicate of your site, one secure and one non-secure version." He recommends using absolute URLs for all navigation and product pages to avoid having multiple versions.