Hi,
In order to downgrade to an older MIUI version or to switch between Stable and Beta ROM or vice-versa, it is highly recommended to Unlock your Phone's Bootloader First and then Fastboot Flash with the respective Fastboot ROM version available for the device via Mi Flash in order to avoid App Force Close and other performance issues.

For Unlocking Bootloader, Please refer this thread : http://c.mi.com/thread-132126-1-1.html
For Flashing Fastboot ROM, Please refer this thread : http://c.mi.com/thread-324489-1-0.html