It's working by themes app...
You have to clear data from themes app, shutdown mobile data and wifi and then choose the option customize.
In there you have the fonts type.
Then you can turn on mobile data and wifi to search for a new font.
How can I contact miui Devs?
Open or search for bug in en.miui.com
Sure and without any problem, if you have the same device and the same rom for sure you can try to install again the rom (without wipe data, wipe only dalvik-cache and cache), if you not fix this, you can try to install a clean rom from the start.