See this screen recording: http://www.youtube.com/watch?v=Wr1BGEyeDZA
Simply put, I had copied an image to my clipboard, typed some text, then pressed "Ctrl+V" to paste the image. Boostnote pasted the markdown-formatted image (as expected) but preceeded the image with some text that I had just typed (in the screen recording, you can see that a couple lines above it replicated the entire line that I had just typed before inserting the markdown-formatted image)