In the above picture you can see a unit of highlighted spearmen in the woods.  You can also see their path towards a larger army.  Also note the road running from the city to the larger army.  

The spearmen were stationed in the city.  I selected them and sent them to merge with the larger army.  Instead of leaving via the road and reaching the larger army the same turn they decided to exit the city via the crystal mine (a square with no road) and then use all their movement going through the woods.  

We shouldn't have to micromanage movement out of a city tile by tile.  There's not legitimate reason for the spearmen to have chosen the path that they did.