[Excel 2010/2013] Bubble Chart fails to update correctly when the dataset is updated

As I change the range of my dataset, in this case by increasing the number of months of data, the Bubble Chart fails to update accordingly. In fact, I lose data on the bubble chart (quite evident by the 3000 point losing its place).

See here: http://imgur.com/a/2TXho

Would appreciate some advice as to why this happens. I make ZERO changes. This is the default bubble graph. All I do between picture 1 and 2 is increase the selection. Picture 1 shows my initial selection.

Thanks!