space isn't freed from HD

I want to get rid of filevault from my home folder, to do this I need to free up the disk space equal to the size of my home folder, so I decided to move files from my main account to Macintosh HD & then to another account which hasn't filevault activated. When I tried to move my files from home folder to Macintosh HD I experienced that the exact size isn't freed from my home folder when I moved them out into the Macintosh HD. I know that I need to log out & log in agin while I'm connected to power adapter to reclaim my disk space. But still I can't regain my exact disk space that I freed by moving the files. Where did my space go ? Please help, I need to get rid of filevault as soon as possible & I think this is the only possible way for me to do it without external hard drive.

Also the filevault tells us how much space I need in my home folder to turn it off. Earlier filevault showed exact space as I kept moving filed, however after moving around 50 GB of data it still tells the same amount of space I need to free from my home folder.

P.S: No files were duplicated while moving, I took care of it. I'm using snow leopard 10.6.8

Is filevault buggy ? It happens as if my disk space is expanding as I'm moving or deleting data.