What's so puzzling? You already know the answer -- NO one-touch -- so GM build in some rest-stops. Here's excerpt from the manual:
1. Using index finger, touch sunroof button
2. Press and HOLD, sunroof will begin to open
3. When rest-stop is reached, lower finger and flex to return circulation
4. Resume pressing and holding button <span class="ev_code_GREY">*</span>
5. Repeat until sunroof is in the fully retracted position
6. Congratulations, you have successfully openned your sunroof!
<span class="ev_code_GREY">(* Optionally you may want to continue using a different finger or even a different hand. CAUTION: Do not use middle finger if the driver behind you is bigger than you are, or is a cop)</span>
