I have version 5.0.PRE.3104 and it is up-to-date according to WowMatrix. Every time I scan the AH the game freezes on me and I have to use Windows task Manager to end WoW.
It completes the scan and then the game freezes. No music to tell me the scan is done. Nothing else happens. Am unsure of the progress bar. I've waited for at least a couple of minutes because I know there is a delay between the end of the scan and the music that plays and to see the results.
assuming you are using AA, go into the options and turn the priority bar down to 50 or even less, and see if that helps things. it will take longer to complete the post scan processing, but it should unfreeze your screen.