Screen font

[Bobxy]

Every once in a while, I hit the back button while typing a text or email on my moto x and the font size enlarges and also displaces the keys on the virtual keyboard. I then must abandon the text as there is no way to get it back to the original size or to continue typing in the larger font. It is driving me a little crazy and would appreciate if someone could tell me how to avoid in the future. Thanks.