When im loading files, sometime is after load file automatically flagged as changed. I dont know why. I dont make any changes,its after load 
Can anyone explain this behaviour to me ?
Change flag onload ?
It depends on your save settings for Mp3 files, by default an ID3v23 tag is created for the file if it doesnt exist, and ID3v22 and ID3v24 tags are converted to ID3v23. This is because ID3v23 is much better supported by other software and because it makes sense to have your music standardised to one format. So if the format is cahnged on load the file is marked as changed.
But you can change all this in Preferences/Save/ID3 Tag V2