It was planned that way.  Also, the reason why there was fighting all the way up to the end is some commanders wanted to capture more territory and have better positioning on the battle field in case the armistice didn't hold and fighting resumed.  Stupid as it may sound some units didn't want to carry the left over ammunition back so they kept firing.  Guys forget the armistice was just that.  A halt to the fight which could have resumed.  A peace treaty wasn't signed June of 1919 and durning that time they had to extend the armistice three times.