You mean, you can add codes to boxes that you can create by click+drag? In that case, you’re seeing the image coding interface. It should only appear when doing click+drag on images, such as the one at the top of the post. If you’re seeing it on normal text as well, we have a bug.
For me it appears only for the first image, so that bug probably is due to your browser. Try in latest Chrome if it works (it does for me), and if so tell me what browser it does not work in so that we can reproduce and fix this.