be sure to set "clip cam". it's the button on the top right of the menu, where you can switch between the clip cam and the free cam. if you are on free cam and move around, the parameters will change only for the free cam, so when you put a new key it won't have done anything to the clip cam, which is the important one for you.
i think that's your prob. or maybe it was having set "Interpolation" set to "none" on the key before the new one...i remember there was an issue aswell...well, just try it out, if it's not the first suggestion, then i'll get into the interpolation one xD