The change I am referring to is that Apple has made the newest iPhone models pick up your voice from the mic on the headset (such as the S4i) and feed it back through the earphones on the headset. So the audio coming through the headphones is both your own voice and the caller on the other end. We have tested many products and the behavior across all that we have tested is the same. It may seem more noticeable using the S4i due to the better seal you get when it is in your ear. When the earphones are not sealed in your ear as well, it is less noticeable because you can hear more of your own voice.
There is nothing that Klipsch, as a manufacturer of Apple certified headsets, can do to correct this. In order to create a 3-button headset that works with an Apple device, we use components that we must purchase from Apple to enable that compatibility (all manufacturers from Klipsch to Bose to Skullcandy use the same components from Apple). Thus, all of the functionality is built into those components by Apple and Klipsch is not able to change it in any way. These are the identical components that would be used in all other Apple certified headsets.