How come everytime I upgrade Buddypress, it deletes user blogs?

Thank goodness I'm just playing around at the moment with a few Buddypress sites and have no users, just sample blogs, but I noticed the last 2 times that I upgraded to the latest version of Buddypress , it deletes all user blogs.

Why is this? Seems like a known glitch that could have been fixed by now.
Is this the way it's always going to be ?