Not BPs, but my garters do it. I think it's got to be some sort of hormonal thing that affects nearby snakes or something because it happens way more than you'd think to just be coincidence.
Very interesting. Perhaps a gross comparison but in a funny way it reminds me of menstruation. Happens to everyone in the house at around the same time and they all get crabby.
I have 18 for example, and when one starts shedding normally 3-4 will go within the next week or so.
I don't believe its a hormonal thing, its more of a: "I keep all my snakes on the same feeding schedule, so they are all growing at the same rate" thing.