When a keyboard is open and the user touches another textfield on the screen, the keyboard will flash quickly like its being closed and opened quickly. But when the user now types on the keyboard the text will not appear in the textfield. It works fine if the user selects done or cancel and then goes to the new text field.
The keyboard does indeed flash briefly just as you described, but the text types in fine on a quick test project that I made. Could you submit a bug report on this issue?