I did it once on an A320, was putting in a fix reference and accidentally dropped it in the NAV UPDATE field with a bit of a spasm that hit the button twice, MAP disappeared and Captain swore a bit. We selected HDG, realised we were out of ALL VOR/DME range and after a minute of wondering what to do simply asked ATC to vector us over the closest WPT and tell us when we were crossing, another NAV UPDATE at that point and off we went :-). I bought the beers that night,