Object Binding And Validation - Value Type Nullables?

Using VB 2005. I am attempting Object Binding, with a validation class that handles the validation at the object properties. But, it is working fine for strings only. For any numbers and dates fields on the form, if I simply enter and leave the text box without entering any data, the validation doesn't kick in. It does only when the text box is dirty (an empty string ?), if I enter something and erase it (backspace), the errorprovider is not letting go unless I fill in something that conforms to the data type of the text box and says the input is not in the correct format / type. And at this point, the object property is yet to be assigned any value, and hence my validation class is yet to activate and do its job.