A bug has been noticed by many users with functional Android 5.0.1 Lollipop, as this causes a lot of memory consumption.
This has some unpleasantness Results as it closes the open ones applications and it does continuous reloads of the original screens.
In Android Issue Tracker of Google, it seems that several devices Nexus have been affected by the above bug, such as Nexus 7 (2013), Nexus 4 and Nexus 5.
While it is normal to consume the device around 500MB, in some cases the bug has consumed up to 1,2GB RAM!
Perhaps this is one of the reasons that very quickly Google moves on upgrade on Android 5.0.2 already released for Nexus 7 (WiFi version) and soon expected for the rest of the devices Nexus.