It's not a bug.
Quick save is used for when you wanna possibly quick load the game from a certain point while it is already in progress. Like you died doing something stupid or made a bad quest choice and wanna quick load from the last quick save.
Regular plain ole' save is just that. When you restart the game tomorrow, your save game will be loaded.
Peacemaker is right about loading the quick save from the load menu.
Just do a usual save when you quit the game and you'll have no problems when you go back to play later.
