I'm not sure that I understand what you are trying to achieve.
When you click or set the focus to the textbox the cursor should appear.
When you update the text in the textbox it doesn't appear at all.
I am trying to write program like flashcards. Two cards on the form, the first is question, the second is answer. When I click empty 'Answer' TextBox answer should appear on it. But when clicking a cursor blinks for a moment then disappears. It is not so fine as I want. Sorry for my English. Thanks.