the problem is audio related. When you get an item, it plays a sound and the game waits for the message that the sound stopped to play to continue. Since sound in Nintendo games isn't emulated, the sound never plays .. so it can't stop (so the game just waits forever for a sound not playing to stop). There's a patch for it, there's a certain instruction you can cancel that will make it go without problems.... by dolphin's lack of patching system... it can't be done that way.
The GCM itself would need to get modified...