Ok, I'm using IE and if you are replying in the "quick reply" box at the bottom of a thread, when typing a reply and you reposition using the mouse or the arrow keys, the cursor ("|") on the screen does not move to reflect the correct position. However, once you start typing again, the current cursor position is updated with each keystroke. Certain other keys, such as the "delete" key can also cause the cursor to disappear.
Strange things also happen to the cursor display if you move the mouse pointer into or out of the text box. If you are typing with the pointer inside the text box, when you move the pointer out of the box, the cursor disappears. If you are typing with the pointer outside the text box and move the pointer into the box, the cursor disappears..