This is an old thread but the best I can find on the topic to date.
I keep my 200GB of music on a NAS and am also pulling my hair out trying to solve this reset issue. I understand that since I sometimes sync my itunes (as my iphone needs calendar and contact information on a regular basic). I use a Macbook because I need it to be portable (this is why it is possible to sync without have the NAS mounted). This means I often do not have my share mounted and iTunes is systematically resetting my default media location.
When I get home, and sync with my music store (the share mounted), my music is now present as should be expected, but the default setting has been changed. Worst of all, I have to put it back, and then off goes iTunes organizing all my files, rebuilding Genius (and maybe other things, again, which takes at least a day).
In a perfect world, itunes should just ignore the bad media location reference or ask me where it is, but not just change it to garbage. This complaint is all over the forums still and therefore, wondering if there was a better fix out there, an idea or should I just wait until Apple hears us?
Thanks
Stuart