Setting the RoT's persistent boot preference from A to B to A to B has unexpected results.

In drv/lpc55-update-server/src/main.rs:

let bit = cfpa[offset][0] & 1; // Reads from ACTIVE CFPA page
let new_bit = if slot == SlotId::A { 0 } else { 1 };
if bit == new_bit {
    // No need to write the CFPA if it's unchanged
    return Ok(());
}

This check for a redundant setting does not take the SCRATCH CFPA page into account.
Every request to change the persistent preference that is different than the active page will result in a write to the scratch page.
Every request to change the persistent preference that is the same as the active page will result in no write to the scratch page.

The caller, via MGS, will get an Ok(()) acknowledgement on every request which may not reflect reality.

Start in drv/lpc55-update-server/src/main.rs at the redundant-setting check shown in the issue, then trace how the active and SCRATCH CFPA pages are handled for persistent boot preference requests. Exercise the A-to-B-to-A-to-B sequence and verify that acknowledgements reflect whether the requested preference was actually written.