ITunes is duplication my purchases and clogging my hard drive

Question

Hi folks, it doesnt sound critical but this is my situation:
I have a rather large music collection so ever since I started using iTunes I have always had my music on an external drive(a NAS more specifically). My music library has always been 'z:/music' and not the default itunes library on the C:-drive ever. Of recent days every purchase I've made has suddenly began downloading it's files onto the iTunes folder on the C:-drive and also it has been downloading files onto my z:/music folder. What has been happening specifically is this: say I puchased and downloaded the movie 'Burn After Reading', a file is downloaded into my C:/my documents/my music/itunes/Burn After Reading.m4v, also a file is downloaded to my z:/music/downloads/Burn After Reading_Joel Coen&Eth.tmp/download.m4v. it is also accompanied by a 'Info.Plist' file.
I go to iTunes and 'check info' on the file displayed in my library and it's destination path is the file contained on the Z:-drive. I also recheck my preferences just like it always has been, my music folder is still 'z:/music'.
I'm trying to figure out why iTunes has started saving my downloads with such an obviously silly name, after all I now have a collection of 'download.m4v files contained in various folders with no sensible way to know what the files are if they are ever taken out of their source folders. And why has it also begun saving what to my eyes is a correctly named file (Burn After Reading.m4v) file to my iTunes folder on my C:-drive.
Most importantly how can I get it to stop. I have simply a huuge amount of music, an enormous and growing collection of audiobooks and a respectable and growing collection of movies from the iTunes store. The PC I run itunes from has been deliberately kept as basic as I can manage and besides application and operating system updates there have been no changes to it's set up quite literally for over 3-years, I use this computer exclusively to download my audible.com and itunes content and thus have learned to keep is simple for the sake of stability and consistency. What do you suppose has happened to it, and again more importantly how can I get it to stop. This machine only has a 40-GB harddrive and it is quickly running out of available free space (3-GB or so) if I make a large enough purchase, like 3-movies a one time I will obviously not have enough available free space to store the files mistakenly downloaded onto the C:-drive.
sorry for the long-winded-ness but thought it best to be thorough..
help!

Answer 1

Thanks, I tried that but it still didn't work.
Just seemed again to resort to the lonely files that are in the default location.
I'm in the process of moving all that again (the folders that I know are being found) and transfering everything onto another partition in the hard drive.
Hopefully that will work but it feel like something is fundamentally wrong. Maybe an upgrade glitch?
Rory