I'm on the Xbox 360 version of the game. I deleted the Dragonborn DLC to reset Teldryn Sero and liked it so much I did the same for the other 2 DLC packs. I was wearing the Locket of Saint Jiub when I did so and now I have a permanent increase to my stamina. The game doesn't say how much in my active effects. It doesn't say anything about Stamina there. but I think it's from the Locket.
Here is a screenshot of my stats.
http://www.elderstats.com/images/cprofiles/photos/4563_456643a7e4c86551aa15a3fdbf8ac877a87e.png
I have yet to re-do the Dawnguard DLC so I don't know what happens if I re-equip the locket. I hope my stamina just stays the same and the effect goes away when I remove the locket.