PR9 Backlinks disappearing over time?

I'v noticed that over the past few months my PR9 backlinks have slowly been disappearing. I used to have at least 8 pointing to one of my websites and over time they have simply been removed. Not sure why, i checked those backlinks and they are still in place as ********s.

Anyone know whats going on with this? Iv checked my competitors websites as well. They have less than they used to have.

It probably has something to do with those pr9 sites wanting to maintain their high level of authority by not having so many questionable outgoing links.