Comment 1 for bug 834449

Thanks for reporting this bug.
This is definitely a regression. The root cause is the extension framework, as the following line:

        ext_mgr = PluginAwareExtensionManager(extensions_path,
                                              QuantumManager().get_plugin())

not only invokes the class method get_plugin but also creates an instance of QuantumManager, whose constructor load the plugin.
The fix is very trivial.

A branch has been attached and proposed for merge.