Admin area question

I am not sure if what I am looking at is making sense, can someone point out if this is a glitch or am I just not seeing this correctly?

On the overview link/tab on the top left of the admin area, near the bottom, there is the area called:

New listings created each month for the last 12 months.

First off, there are duplicated months on my output for that area, so I have a total of 15 months, not 12. Now I understand that this is supposed to be showing New listings only in the last 12 months. Can someone explain the photo I have attached?

Thank you
Brian