This is more of a meta bug. MIUI supports multiple devices, and quite a few of those are older and have less then 1GB of ram. More of a conscious effort needs to be placed on making efficient used of that ram. For my Nexus S with only 512mb of ram even after building a special kernel that give me more system ram I'm having a hard time multi tasking or even using the browser. We all know JB is a bit of a memory slut, and for the past few months the MIUI devs have been adding extra APKs (mostly background services) to the rom releases. This is getting really ugly on my phone. And as much as I love MIUI I think I will have to switch to a different rom until I get the next Nexus/MI phone.