While talking with my wife recently, the friendship level pop-up in the dialogue box shows we have level "13/12":  
[![13/12 friendship][1]][1]  
This seems peculiar, since only 12 hearts out of a maximum of 12 show in the social tab:  
[![12 hearts in social tab][2]][2]  
Furthermore, on the wiki ([here][3] and [here][4]), the maximum friendship level is stated to be 12 for a spouse. From the second link (emphasis mine):

> Once a villager has been married, they will move into the farmhouse. They will have a **maximum of 12 hearts** instead of 10 [...]

**Is there any information from on this (from the developers perhaps)? Is there an in-game explanation for it that I'm unaware of (like a secret 13th friendship level)?**


  [1]: https://i.sstatic.net/zamp3.jpg
  [2]: https://i.sstatic.net/suFM7.jpg
  [3]: http://stardewvalleywiki.com/Friendship
  [4]: http://stardewvalleywiki.com/Marriage