This extension causes dev/core#2729

Hi @DaveD,

Well, there's a reason no one but us can replicate core#2729 - it's caused by this extension, which I'm guessing we're the only two users of. The bug became enough of my nemesis that I decided to track it down no matter how long it took.

The problem happens intermittently because it only happens when hook_civicrm_check is fired - and that's why it seems to happen when visiting the dashboard.

The culprit is this line: CRM_Extension_System::singleton(TRUE);. Creating a new CRM_Extension_System object causes CRM_Extension_ClassLoader::__destruct() to be called, which unloads the classloader that finds the Civi namespace. You can place calls to spl_autoload_functions() directly before and after the culprit line to see the problem.