text cursor glitch

ok sometimes when i type the text cursor moves by itself back into the text therefore messing up what i type, like so:

instead of i went to walk the dog it would say

i wee e dognt walk th to (so happens it did the glitch here when i tried to fake it, in essense this is what it looks like done twice)

done once: i toog for a alkk the do

anyone know what's causing this? it bugs me like crazy

If you're on a laptop, you're probably hitting the track pad. I've done it quite a bit, and it does get a bit annoying.