I just noticed this checkbox in the Additional Security Information under the Security Detail Page. I've never seen it before; perhaps it is new. I can't find any mention of it in Help.
This may be the solution to the long-time problem of TIPS and (I've read) some amortizing mortgage bonds having incorrect prices reported by Schwab and Vanguard. For my TIPS, I manually enter the month-end price from Treasury Direct, but unless I remember to set the date on my portfolio to that month-end date, the correct prices are overwhelmed by the incorrect prices downloaded from Schwab every day (prices that ignore the inflation factor). So I need to manually go into the Price History for each bond and delete all the downloaded prices, so the price I manually entered can be used to determine the position value. I've never found a way to prevent prices for selected securities from being downloaded from the broker when I do a one-step update.
I'd love for this to be a fix for this problem.