Something that doesn't seem to get mentioned in the comments is the placing of the trackpad; so near the keyboard. This was one the first things I recognised as a potential err.

I once had a ASUS notebook which had a similar design. The problem was that my tip of one or both thumbs or part of it, often touched the touchpad in a fashion that it selected text if working in a editor. This would happen so fast that my typing replaced the text. Very annoying, so annoying that I bought a new notebook of different brand.

I imagine something similar could happen on the Macbook Notebook.