User blog comment:Kirkburn/Technical Update: August 20, 2013/@comment-3562424-20130822024359/@comment-11733175-20130822105011

The commit would appear to be this, although a small fix was needed as seen here, which fixed all the issues descibed below, such as images not loading, the edit dropdown not working correctly and the obvious mw-collapsible breaking too.

It looks like it was just moving the function definition to be with the other variable declarations towards the top of the function instead of being declared in a conditional. However, understanding how it fixed the issue is beyond my knowledge.