It's not exactly a bug, many versions of the os and even other OEMs have them shut off to prevent overheating and better battery life. Allmost all versions of the MIUI os had them turn off and on through kernel tweaking. Some versions of the beta ROM had kinda left out that part and it resulted in poeple gaining performance boost's and complain about battery life. If you install CPU-z on different versions of MIUI you will see them other offline or online, but installing a kernel app you will allmost always see them online but sleeping. maybe MIUI changed the way cores are perceived with apps, I can't say not being a developer.
Normally it should run on lower core's and then crack up to the more powerful one's when needed. A kernel will manage that transition better or worse depending on the desired effect and the app itself. Running all of them at once isn't something that Qualcomm intended to my knowledge and all I have read online about it. It's possible but I don't think it's required.
People having lag during gameing comes down to thermal throttle because of over heating and poor optimized OS and game's.
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