Charting Legend automatically changes

I have a chart in Excel 2013 that I'm trying to attach a legend to. I have 6 different series in my chart, but i only want 4 to appear on the legend. Once I add a legend to my plot, all 6 series are included, as expected. I click and highlight the two that I do not want and press the delete button. This allows me to to get the plot looking the way I want. However, when I A) save the file, close it, and open later; or B) try to copy and paste the graph elsewhere as an image, the legend goes wonky on me and starts removing some of the series' i had not deleted and bring back some of those i had removed.

How do I control which series' are visible in a plot without this automatic change interfering?