I was translating the page about Eduardo Pérez Pujol. Because his name included an accented character, I copied it and pasted it into my translation, but then a magic balloon appeared with part of his name inside it, in front of my translation, obscuring my text, and nothing I could do would make it go away. When I eventually hit Enter, (thinking to insert a line-feed so I could see what I was typing) the software decided I wanted it to mark my incomplete translation, which, of course, I didn't. Anybody know how I get rid of this, should it happen again?
I've had a similar issue; one way to get rid of this is to click another sentence to translate, then return to the one you were working on. You'll notice DuoLingo retains your unfinished translations as long as you don't leave the page.
NB: I also find it annoying that your (unfinished) translation is evaluated when you accidentally press Enter.