Just reporting news from last official update of china dev rom 6.1.14 : Xiaomi locked the bootloader for mi 4c and mi note pro in the last dev rom, so if you update you will no longer be able to use fastboot for flashing.
If you have a custom recovery the update process will result in a bootloop.
Link to the official changelog
From 6.1.14 root procedure have changed, have a look here
English unlocking method now available
Apply here http://en.miui.com/unlock/
here you can find fastboot image for china dev 6.1.7
https://mega.nz/#!RMJx2ChD!Jfu44Govt...xGC5yJplAxK0YY (thanks to @dirwo from htcmania Spain)
https://drive.google.com/file/d/0B3j...ew?usp=sharing (thanks to @Ulver)
As reported by @person_x and confirmed by @cowithgun you can revert back the bootloader flashing last stable rom from updater app
FOR DEVICES IN BOOTLOOP check this guide
Xiaomi.eu remove bootloader locking from its rom, so Xiaomi.eu and sMiui 6.1.14 roms are safe!