My iphone is still on lock after unlock screen?

I never had this problem, but it happened after my sister put a passcode on it. Its a jailbroken 6ios iphone 4. After sliding the slider its shows the apps and wallpaper for a secound. Than is returns to the lock screen without passcode, shouldni just restore it or is there a soulution?

Do a hard reset (press the home and top button at the same time, until the phone turns off)
Jail broken phones are always problematic.