Magento 1 productpage 404 in developer mode

Question

When we enable the developer mode on our Magento 1.9 store, for some reason all our productpages gets a 404 status. But the page shows all content of the product, but it only gets the body class cms-index-noroute noroute-404.

When we disable the developermode again, it works all fine.

Is this normal and how can we solve this?

We enable the developer mode with:

ini_set('display_errors', 1);
error_reporting(E_ALL);

$_SERVER['MAGE_IS_DEVELOPER_MODE'] = true;

Answer 1

Most likely issue is that an error message is being suppressed when not in developer mode but is triggering when developer mode is enabled and that is causing the issue. As you are not seeing the error on the screen, I would check the exception.log and system.log and see if there is a warning that is stopping the page rendering. Likely to a Javascript call to a now error reporting page.