This is not supposed to happen and I never had such a problem. Without tracing infos, we can't help you.
asking me questions might help its traditionally how fault finding diagnostics works but you shouldnt need me to tell you that if you are any kind of programmer, what would you like to know that I didnt tell you in my original post?
It was trying to read a DATA disk FFS! Surely it should be able to tell the difference between an actual movie dvd & a data disk for a game?
having completed & uninstalled Quake 4 yesterday. I tried to open an AVI file and VLC told me there was "No disk in the drive". Proof if its needed it was actually looking for something to play in there. I cancelled that error message and it no longer appears after a restart of vlc. but it DOES prove it looks for stuff in the dvd drive.