iTunes changes my library location on its own

About 90% of the time I open itunes it has my library location in a different place then where I always set it for (preferences->advanced). I have my library on a time capsule but whenever I open it up it creates a library on my internal hd. It is the same library, it just changes location's. It is very very VERY annoying especially when I transfer movies into itunes and come back 5 hours later to find I have wasted my time because they are now all by themselves on my hd as opposed to the time capsule I wish for them to be on. If only we could post expletives you could then gain insight into how angry I get with this.

Anything?

Thanks

you must must mount the disc before you open iTunes otherwise it will default to the internal