When DCC target folders for *.mid, *.wav, *.mp3, *.ogg, *.wma are deleted in the DCC Options/Folders dialog, mIRC always recreates these entries on startup, pointing them to <mircdir>\sound.
I've noticed that too, it's a pain when you want to make a bot and have the mIRC folder as clean as possible. I don't think it is a bug though. mIRC supports sound (indirectly) so I guess the author just intentionally made it that way.
I solved the issue just by changing the default directory to $mircdir and making sure everything else was turned off so the folder would not fill up with anything. It's a case of as long as something in in the setting then all is well.
yeah, mirc recreates and redirects the sound files to that folder everytime its loaded its annoying, as i want to put my sound files in a different folder, and when you use splay, it references it to that folder