Can't delete libvlc.dll: is in use

I was preparing to install the VLC 0.9.6 update. Normally I'd just install it over the old version, but this time I wanted to delete the old version and install the new.* However, it won't let me: "Cannot delete libvlc: Access is denied."

I did not start VLC in this session, don't have it set to auto-start, and PStart is not autorunning VLC... yet there it is in System Explorer, process vlc.exe is running. In the process details, the Command Line is: "[drive]:\PortableApps\VLCPortable\App\vlc\vlc.exe" -l ntservice --How did it get this switch?

I did once set VLC as the default media player, but removed it because what I really wanted was for the media button on my keyboard to play and pause VLC. That didn't work. It only works with Media Player, so I reset Media Player as the default.

Any suggestions on how I can fix this? It's easy enough to kill the process so I can delete the old files, but I want to know why it's running in the first place. I don't know much about setting up Windows services and I don't want any portable programs running without my knowledge.

*I bought a new 8GB USB key when my other one split at the seams. A straight copy of my backup files onto the new key (using drag-and-drop in WinXP) ran out of space before half my programs were copied over! Somehow the app files gained weight when I copied them, which I verified by reviewing their properties. Some of the apps carried around 300-400MB of mystery data. I finally managed to get all the apps on by deleting all my photos off the new stick... but I shouldn't have had to delete anything, and my old stick, complete with photos, still had over 230 MB free space.

I don't know how those files bloated, but as updates come along, I've been deleting apps and installing them fresh, then copying my backed-up settings over, hoping to get rid of the mysterious extra bytes each app carried in with it, since apparently a straight copy doesn't work right.