A couple of blog posts you might find helpful:
http://www.thegeneticgenealogist.com/2009/11/10/qa-everyone-...The above post is an important one. DNA inheritance is random and quirky and uneven. While you get an equal share of your parents DNA, it is possible to not get an even 25-25-25-25 of your grandparents. And once one branch slips more or less, the branches further up will also skew one way or another. I can see this in my own testing: in comparing me to my paternal grandmother (using tools not available at Ancestry since I have uploaded all of my data to FTDNA and GedMatch) there are 3 whole chromosomes where I share absolutely no DNA with her -- therefore on those 3 all of the DNA I got from my Dad came from his father. Vice versa there are 2 chromosomes where I match her completely so there was nothing from my grandfather there. In total I actually share about 23% with my grandmother instead of 25%. So I will have less DNA from her branches than from others.
http://www.legalgenealogist.com/blog/2014/05/18/admixture-no...This post points out that ethnicity predictions are not that "scientific" yet and might never be. Each testing company has its own set of reference populations, and they vary greatly. Combine that with the above information and you can see why so many people can be puzzled, amused, confused, or/or intrigued by their results.
Elizabeth