Modifying Rooms
 

This might be an obvious answer, so apologies if it is!

With flexible rates, every now and then I'll check if the room rate has changed using the modify button. This will then show all rooms available and the cost, with the option to change to that room/rate.

Some bookings however don't show all the rooms. They just show possibly one Upgrade option (to a higher room) then payment information immediately below it. Even when rooms are available to modify the booking to.

In fact when I go into the booking there isn't even a modify or cancel option. It doesn't show my current booked room, just the payment information.

To be clear, these are all flexible bookings that can be changed.

Is this a website bug or are some hotels/bookings like this by design?