Cursor jumps back on DELL computers

I have an XPS Dell compute bought only a few months ago and since I opened the box and use the computer I start  having this fustrating and annoying issue:  when I type an e-mail, a letter, a document, or simply chat with friends, the cursor just jumps back at any point of the previosly written text or paragraph, messing up everything and making a real mess because it is all mixed up making what I previously wrote impossible to read. I previously had an Inspiron 1525 with the same issue; when I called dell support they send me a technician to change the keyboard, but nothing changed. I assumed it is a factory problem from DELL. I have other two laptops, an HP and a SONY and never had these issues.