The MathOverflow user -1 occasionally bumps questions from the Unanswered list to the front page. How does this "random" process work, and is it really random?

I became curious because, possibly by coincidence, I have a question from February that I think has been bumped at least 4 times, whereas browsing the Unanswered list shows many questions that haven't been modified in a long time, indicating in particular that they haven't been randomly bumped. Is this all part of the expected probability distribution, or are some other factors taken into account when user -1 decides to bump a question? (I have no idea what those factors might be...)

I'm not interested enough to try to analyze the data versus the expected distribution myself, but it would be nice if someone who knows how the software selects questions could explain that here or point to a place where we can read about it.

Also, it is a shame to see so many old Unanswered questions being neglected by this process. Would it be possible and desirable to modify the process so that older Unanswered questions by recently active users are given preference in the selection process?

Updated July 17: This is clearly not a pressing issue, but that same question has been bumped twice more since I posted. I'm not complaining! But it seems far from random.