Line and text disappearing when scrolling

[RSpisketts]

Hi,

When I am writing text to a text field and the text is about to go off the bottom of the page, I scroll down (as you do). However, I get horizontal lines appearing where the base of the window used to be.

Also, if I carry on typing (so the window scrolls itself), some lines of text seem to disappear (they haven't actually gone anywhere and you can click outside the text box to make them appear again).

Is this a known problem ?

Has anybody had it before ?

Thanks,

Roger.