Lutheranism: "Pastor" or "Priest"? I have noticed that some Lutheran churches refer to their ministers as "priests" while others refer to their ministers as "pastors."

When did some Lutheran churches cease using "priest" in favor of "pastor"?

What is the foremost reason for this change in terminology?

Conversely, why did some Lutheran churches continue using the word "priest"?
While there are a few exceptions specifically within the Lutheran Circle - Pastor - is used to show the role as a shepherd however it is an exact replacement/translation depending if used in another language other than English for the word Priest. 

It is important however to understand that Lutherans for the most part do believe that each Christian has the authority to preach and teach, read and interpret the Bible, and confess their own sins directly to Jesus. (Universal Priesthood)

Is Universal Priesthood Biblical? 

The Bible teaches that all believers have priesthood authority (1 Peter 2:5, 9; Rev. 1:6; 5:10; 20:6).  

Even in the Old Testament, the nation of Israel was to be a kingdom of priests (Ex. 19:5-6).  However, Jesus is the unique High Priest (Heb. 7:23-8:13).  

Lutherans hold this to be true - that each believer has the authority to preach the Gospel.  Of course Lutherans still have professional clergy and therefore most often are called Pastors.

If you were to visit http://arc.episcopalchurch.org/ministry/oepp/oepp.html
you would see that the Episcopal church and the Evangelical Lutheran Church in America see both as the same as they now have agreed to allow "pastors or priests" to exchange (ie borrow from one church to be used in another) between the denominations.