Weird Windoze Problem

[mrlynn]

My wife's computer runs XP Pro (SP3). In any application that uses word processing, mainly M$ Word and Thunderbird, occasionally when she attempts to insert a letter into a word, the software starts deleting the next letter. Say, adding an 's' to 'bookih' (to make 'bookish') yields 'bookis'. This bizarre behavior persists until she quits out of the program. In a Word document, if you copy the text, close the document, and open a new one, the program behaves correctly—until it happens again.

Any idea what causes this behavior, and how to prevent it from happening? It's very frustrating when it happens in the middle of a long document.

/Mr Lynn