I was recently looking up which countries were in the Congo Basin, and the version of the article I found was this:

http://en.wikipedia.org/w/index.php?title=Congo_Basin&oldid=359085351

The list of countries is clearly missing.

It was removed with this edit:

http://en.wikipedia.org/w/index.php?title=Congo_Basin&diff=357222409&...

That was 20 April 2010 (I've now restored the list).

Has anyone done a recent study to see how and why vandalism like that is missed and how common it is for such things to be missed?

Carcharoth