This is a serious bug.
There should have been a warning.
PHP is used to manipulate data, and as a result, we have some cookie data for users that was set to PHP code strings.
Luckily we do most of our data cooking in dedicated plugins of our own, but we did have some items in A/B testing using this plugin and those user cookies are now polluted.
But it took us some time to track down the issue. We noticed the change in this plugin’s settings, but when we set the option it did not appear to resolve the problem. It took us some time to realize that PHP strings were now stored in cookies and being pulled back into the page environment. We have now had to implement new code to check cookies for PHP code and zero values if they contain PHP code. So we had to write net new code to undo what the change in defaults did on our site, and we have lost user data.
NEVER release a change in fundamental behavior unless you:
- DEFAULT to old behavior and make the new behavior an option
- Provide a WARNING prior to upgrade about what will change; word press provides a space for banners in the plugin list for this reason