Michael Sync is trying to
solve a problem with UpdateSourceTrigger which is not supported in Silverlight until version 3.o.
You will need to set the focus on other controls and re-focus to the control that you are using. For example: You are typing in TextBoxA. You want to have UpdateSourceTrigger support for that textbox. So, what you have to do is that you need to change the focus on another control (e.g. TextboxB) and re-set the focus on TextboxA while typing.