The bug was primarily in the calendar app that resulted into increased network activity thereby reducing the battery life. Apple said that the iOS 6.1.2 will take care of "an Exchange calendar bug that could result in increased network activity and reduced battery life."
There is no news as yet from the jailbreaking community especially the evad3rs group whether their jailbreak tool evasi0n will work on iOS 6.1.2 or not. Just a week earlier evad3rs updated their jailbreaking tool to support iOS 6.1.1 update. iOS 6.1.1 was released by apple to fix 3G connectivity and battery related bug in iPhone 4S.