Whenever I start Amarok, all files in my playlist show the "This file is not in your collection" thingie... They read just fine ─they don't turn grey─, and scores and all sorts of info are kept updated. So, it doesn't lose paths or anything, it only "forgets" the collection. It shows no errors though, so no debug info is available.
When I configure the collection (again), all folder I had selected are not selected anymore. I add them, update collection, everything works perfectly... until I restart Amarok (on reboot actually, since I don't quit Amarok.)
I read somewhere that perhaps using links is not the best choice ─although I have always used links without ANY trouble─, so I tried configuring them as direct paths: still the same problem. Amarok forgets my collection every time it starts up.
Permissions are fine, since I own the directories and files (rwx for me).
I am using Amarok 1.4.10 (uses SQLite I believe, since I haven't the choice to use PostgreSQL/MySQL), on a Slackware 12.2 system (2.6.27.7 kernel).

Any help would be much appreciated.
Thanks in advance.

Well... it hasn't actually been fixed nor solved, but I no longer require a solution. I woke up one morning and though the root of the problem could be a local configuration bug.
But I didn't find any ~/.amarok folder ─or anything of the order─, where are Amarok configuration files kept?
So, the only solution I could think of: new user. Amarok is no longer amnesiac about the collection...
Although erasing my former user's configuration files would have saved me a few minutes...

Config files are  ~/.kde/share/config/amarok* and the amarok directory is ~/.kde/share/apps/amarok/

Yep, usually if a new user account works, the probability is good that there's an issue with the config. If deleting Amarok's config doesn't work, the problem may be in KDE settings, although your symptoms do sound amarok related. One thing that can cause odd collection issues is having your music on a removable drive - they're not always mounted in the same place, but you sound like you're on top of it