I had this problem previously with no idea how to correct it... until now, that is. I was originally opening sims3packs on my desktop. Sure, they show up with the success window and everything but once the launcher quits, it uninstalls itself. I now place them in the Downloads folder in My Documents and it works fine once everything is decrapified and such.
As for your problem, hellknowsimcoming, do you happen to have sr3c.exe and decrapify.exe in the Downloads folder? That's how my setup is and everything shows up fine in my game, including the More Magic Set.
I always put all my sims3pack downloads into the downloads folder before even installing them. Yes they are in there and it's still not working.
@jeromycraig what do you mean when you say "don't do that thing you did 4 days ago?"