I tested this here:
Drag & Drop an image into the editor
then click into the editor at the very top.
the cursor is "blinking" in the very first line within the editor.
then write some text.
the text you are writing is not showing in the very first line (where the cursor was blinking before you started writing your text), but the text is showing up below the image.
It is somehow similar to this one:
Using Win8 / Firefox 21.0