Today we will open 28bps lower than we ended yesterday. That
means we will open at 100.85 after closing at 101.13. This was due
to the bond rollover.

What is a Bond Rollover?

Well, it's an event that happens around the 10th of every month at
which time the current month's coupon is closed out and any new
loans are placed with next months coupon.

PLAIN ENGLISH:

When lenders are selling the mortgages that we originators close,
they are selling them forward to be delivered. So if you close a loan
in June, they are pricing that into July's coupon. The Rollover
is when we start promising coupons to be delivered into the next
coupon, in our example's sake for August. There are multiple coupons
running at a time (confusing isn't it?) so we adjust our tracking to the
proper coupon. The new price is what investors are paying for that
month's coupon. We don't have to worry about that affecting the rate
sheet, that is the bottom line.