ricky...it can happen
1) when you hit 'reload', instead of waiting till your post is done and then clicking on it...or
2) when your connection seems not to be working and you hit 'enter' several times trying to make it work...or
3) when you accidently hit 'back' twice and then enter...and I think it can happen
4) because of some of the eccentricities of Internet Explorer....

and I think it can happen
5) because of Gremlins!!

3) has happened to me....and I believe also 4)

(oh...also...you gotta hold your mouth right!)