Retagging externally stored files

Hello.
Can anyone explain why, when I retag any files stored on my external hard drive (where I keep all of my MP3's), it doesn't actually change at base level, but if I drag them onto my internal drive and retag it does?
I am using iTunes to do this, and selecting the files individually (or globally if it's an entire album title).
It just seems strange, and is a royal pain in the bum, as I have to remove them from iTunes, reselect the import to iTunes library option, retag, move the files back to the external, deselect the import to iTunes library option, and then drag them back from the external drive. Long winded I think you'll agree.
If I do the retagging with the files on the external still, it shows as being done in iTunes itself, but if I remove them and import again, they revert back to the original badly tagged file.
Any ideas? Thanks!

(Ps: I wasn't sure where to put this, so please move it if it should be in the software section)

is your external from a pC and formatted in Windows NT file sytem (NTFS)

and have you set-up iTunes to use that external as the source for all of your music, or have you just deselected (let iTunes manage my library)

louishen said:

is your external from a pC and formatted in Windows NT file sytem (NTFS)

and have you set-up iTunes to use that external as the source for all of your music, or have you just deselected (let iTunes manage my library)

Click to expand...

No, the external is formatted for Mac, and iTunes is set so that it does not import to the iTunes Library. The only time it does is if I import a cd.