I'm not 100% sure, but I got two moved forum alerts when I assume the thread had already been moved to the resolved bugs forum.
I can't tell if this was moved...
Also, your regex has a case insensitive match option but you are testing for img|IMG bbcode tags.
Additionally, that regex will fail on the new XF2.1 [img] format. Example; [IMG align="left" width="337px" alt="PHP versions"]
Most callback locations standardize the method name via $method = 'get' . \XF\Util\Php::camelCase($offset); (ie entities or controllers), but approval queue does not, it uses $method = 'action' . ucfirst($action); which is unexpectedly different.
Worse, LogicException: invalid_method is thrown...
I work in IT, using beta code in a live environment is a fact of life. The difference between a version stamp of "1.0.0" and "1.0.0 beta' is basically non-existent.
The version string sadly has very little to say on how production ready code actually is.