This happens because the heel of your palm is resting on the trackpad, registering as a mouse click. This is also why an external keyboard solves the problem,.
There are only a couple solutions.
1: Train yourself to have better posture when typing, which may also help avoid RSIs like carpel tunnel
2: Always carry a keyboard with you
3: Some trackpad software lets you automatically disable the trackpad if another mouse is present, so swap "mouse" for "keyboard" in #2
I personally wonder why all computer makers put the mouse dead center. Why not off to the right hand side? Instead of a numeric keypad on widescreen display laptops, they could easily just put the trackpad up there. Would actually better simulate the desktop experience. Maybe some day that idea will catch on. Apple actually did it with their first laptop. You could even swap the keyboard and mouse's position to make it lefty friendly. Somewhere along the line that idea got lost.
Does anyone know how to stop the cursor jumping all over the place when you are typing on a laptop. Can be typing and then suddenly it jumps and you are typing somewhere else on the page. I have been using a plug in keyboard which solves the problem but isn't always convenient to carry. This is the first time I have typed without it for ages and it hasn't done the jumping maybe it has fixed itself!!! I have a Dell Inspiron 1525.