yesterday i download MIUI theme and when i try to change theme it ask me to reboot and when i accept to reboot the rom fail to start again and the only way to reload it is to do factory reset again that was so so bad it cost time .
so my advice don't try to change theme now till final release.or solve this issue.
I believe you have tried theme which is not compatible with MIUI V4 version.
I did the same wrong thing. So suggest to everyone not to use any old theme.
Anyway friends ive made some changes the V4 lockscreen...with battery charging animation....
Plz find the attachment....& have fun