Jenny, here is a full list of post were rand and other SEOMoz associates talk about the updates to the mozscape index (which powers OSE and the pro tools):
http://www.seomoz.org/pages/search_results?q=mozscape+update%3A
In regards to your question of what is mozscape here is another great resource:
http://www.seomoz.org/help/what-is-mozscape
In regards to your last question, it sounds like it was a blend of you losing some links and the mozscape fluctuations. Always take OSE data with a grain of salt, that information is simply to give you insight to trends in your link profile. Did your domain authority drop or stay the same during the changes?
- Kyle
