Today I upgraded from a preview build of OS X Yosemite to the GM Candidate #1 (14A379a). I'm using Alfred 2.4 (279).
When i try to open the iTunes mini player in Alfred, nothing appears, and Alfred is then unresponsive. I can kill the process and start from scratch and Alfred behaves normally as long as the mini player isn't invoked.
I tried rebuilding the music index and artwork index, and the 1st time you invoke the mini player after that it pops up the window where it goes through indexing, but then it gets to processing artwork and it hangs forever.
Everything was fine in the previous preview build of OS X Yosemite. I don't have the build number available.