To put it politely your post is total and utter crud. I'm not being defensive, simply stating facts- MC has it's flaws, and I'm sure most users would admit that.
There is no way MC is calling 18 Vobsub instances, something is plain and simple wrong with your setup.
Auto-import runs a max of I believe 4 (I stand to be corrected though) concurrent file analysis threads, this is certainly true for any manual audio/ video analysis, and these are used to pull off the duration, dimensions and a thumbnail- Basic information, nothing more.
Why is it auto-scanning? Because the main feature of MC is it's library and database.
Other players do different things better (I'm not getting into that argument), but MC's main attraction is the strength and flexibility of it's database. The development team have decided it makes sense to automatically trigger an import to populate the DB.
There is also a prompt which asks you for confirmations and details, which you convienently seem to have missed!
Actually give us some hard facts (System specs, OS, codecs installed, AV checkers, other background software), and we might be able to help, rather than simply slagging off MC-
My money is on a completely crapped up codec installation. Manually installing a combination of random codecs is simply asking for trouble. I've come across the odd unreliable DirectShow filter, but this bears absolutley no relationship to whether it's open source or not
-Leezer-