I don't understand what the error is? Can you clarify?

Ah, I see what you're referring to. Postponing the top break sets the due time to the postpone amount, but postponing the second break sets it to a longer interval. This is the expected behavior, if you have the option enabled to skip the break if a higher priority one is due within a time interval. The top break is the highest priority one, so subsequent breaks are rescheduled if they would be due too soon.