Hello,
Thank you, Peter, for helping during this situation with WP 4.2.3 and the new Shortcode API.
The temporary fix above is definitely not recommended. Core files should never be modified, and it was my mistake to propose it. While it brings back the previous behavior of shortcodes, it reopens the security vulnerability that was addressed by the WP 4.2.3 update.
For everyone still having shortcode issues with WP 4.2.3 compatibility, please tell me how you’re using the shortcode (and surrounding context) so I can solve it in a plugin update – that would be the correct way of solving the issue.