Default L9 storage question internal/external


I have installed MIUI on my L9, and 16gb sdcard.

I see very strange thing. When i use memory of my External sdcard and try to download/delete something from here (ex. apk 40mb) my INTERNAL memory gets more free space.

This is normal?
I didnt see divide of types of files on EXTERNAL memory card in options of memory. Only see this with internal card.
Dunno what is this but have problems with installing or downloading somehing items on external card, becouse internal card think i download to internal memory.

sorry for my bad eng.
please help, i cant install bigger programs, even backup from external card is see in memory of internal card.

My phone in internal memory have only 500-600mb storage busy, but phone "think" and show me i have only 700mb from 2.5gb of fre space becouse other files on external memory phone thinking is on internal.

how can fix this??
before have samsung/motorola/htc phones and didnt have this problems...