When you are writing an expire time (i.e. not one on the drop down), and you already have one in your browser's suggestion box, and pick it from there, the "uneditable" move time below does not change, but rather stays at the text you original wrote (e.g. usually just a number).
A suggestion is to change the other box upon lost of focus from the other box or when the additional reason box gains focus (which might be afterwards). It should still be possible via JS to detect whether the move protection is simply the same as above.