Why is the Silverlight button hard to click when I touch the HP Touchsmart?

Question

I use Silverlight to develop an application that we expect will be used on touch monitors in healthcare settings. I find that simple controls, such as Button, or even simpler primitive controls that I wrote to capture mouse events, are very unstable and do not respond to HP Touchsmart. Many times, clicks are not even recorded, but the behavior is completely unpredictable.

Any idea why a simple Silverlight button is hard to click by tapping the HP Touchsmart?