Every time I type on my laptop something happens or I press something that makes the cursor go back a few words. So I would be typing a sentence and half way through it would skip a few words back and make me insert letters into another word. I could type, The dog was happy. The cow was...
if the laptop has a pointing stick (between b g h and n keys) or a touch pad, you may brush either of them with your fingers or wrists that make it think you want to select another part of the text to insert text to. it happens to me a lot on an asus netbook when i type an email in bed.
You need to examine more closely what is happening. For example... you assume you are pressing a key or something to make the cursor skip back. Is the cursor coincidentally skipping back to where the mouse is on the screen? If the mouse pointer is also sitting where the cursor is skipping back to, what you are doing is quite common. What is happening in this case, is that you are accidentally brushing the touch pad with the meat of your hand while you are typing. This is considered a tap, and would be the same as if you clicked the left mouse button while typing. This has become almost an epidemic, and Touch Pad manufacturers have gone so far as to re-make their hardware drivers, to disable the touch pad while you are typing to avoid just this issue. So... you can download the most recent drivers available from your touch pad manufacturer (Alps, Synaptics, etc) or from Sony... or learn to hold your hands in a slightly better position while typing.
The left arrow key would do that.
