Brawl/P:M Slowdown Issue

[Kurausukun]

When playing on stages that have multiple "parts," the game always lags when loading that part. For example, it lags horribly between the transitions of Castle Siege, and Spear Pillar also lags when loading Dialga/Palkia/Cresselia (this list is obviously not exhaustive). Is this known/is there a way to alleviate it? By the way, I've only tested this on P:M, but I'm confident it happens in vBrawl for no good reason :P