Touchscreen Protector and Sensitivity

I have Samsung Spica I5700 that have capacitive touchscreen, and I used a touchscreen protector. Recently, I've noticed that the touchscreen often produces erratic movements, for example, if I put my still finger on the screen, the "cursor" will shake vigorously (sometimes very far off). This makes the touchscreen very unusable; countless of times I've accidentally flinged the page when scrolling, while touching the screen for small scrolling; countless of times, the screen registered scrolling as a zooming or unzooming; and worse, it often flings to the wrong direction from my swiping direction (indicating a random erratic sensing). Sometimes, when I tried to touch a button/link on the top-left, the screen will detect a click in some other far away button (i.e. one **not** under my finger). Any games that uses touch intensively also becomes unplayable. Could this be caused by the screen protector? Since capacitive touchscreen is operated by soft surface of a finger (instead of a pointy stylus), is there any noticeable benefit of using screen protector? or are they just a waste of time and money? do you think peeling off the protector will have a chance of fixing those problems?