Files being deleted and / or locked

I was round at a friends house yesterday who has been having website problems and some VERY strange things where happening.

This is on the latest version of 2.x & 3.x as I uninstalled 3.x and installed the latest 2.x during the problems and it continued.

Using windows vista

I would amend a file in dreamweaver, upload the file via smartftp to the server, check the webpage out and on noting i need to to make a change, make the change, press SAVE and it would say the file is locked, then when I look in the folder the file has been deleted. The file is still open in dreamweaver has to be saved as (IT's NAME plus the html extension).

Can anyone explain if this is a smart ftp problem, vista or other....???

Thanks Ian