Plugin UserGroups doesn't work since piwik 2.14.1

We use the plugin UserGroups to manage all the user rights of our piwik instance. Since the 2.13.1 update, this plugin doesn’t work anymore.
The administration page of the plugin is still working but users have no rights after login.
We find a workaround by modifiying the following function in core/Access.php :

[attachment 2371 getInstance_function_modified.PNG]

The problem is still there in last version 2.13.3 and I can’t find any issue about this problem in the issue tracking.