As I said, since I upgraded to iTunes 5 (or 6, or maybe earlier for other users), when I double-click a Clutter album record, iTunes starts reading it from the middle.
Turns out there was no need to load the source code (though I finally managed to), as the AppleScript files are directly accessible from within the application.
So, if you like Clutter (and there’s no way you shouldn’t if you’re using iTunes on OS X) but find it unusable because of this bug, here’s a fix: ctrl-click (or right-click) Clutter.app, choose “Show Package Contents”, open “Contents”, then “Resources”, make a backup copy of the PlayArtistAlbum.scpt file and replace it with this one (this is a zip file — you’ve got to double-click it first to uncompress it). Relaunch Clutter.
Warning: I fixed it so it worked on my machine, but can’t make any guarantees as to whether it’ll work for anyone else. Which is why you should have made a backup copy first.