I sometimes run into problems when trying out stuff with the servo settings because the slider only updates values when it is attached.
In my case the shoulder servo had a previously set value of ? and was moving up freightingly fast towards my head. Detaching the servo stopped it. But then the slider is not "acitve" and moving the slider in detached mode has no impact on the servo target. This means that when setting the slider to 30 in detached mode and attaching the servo it will still move to its previous value (in my case maybe 90 or more).
Only when the servo is in attached mode the slider will be activated and the arm moved back to its rest position.