NTSC GameCube game on PAL Wii stuck at 50hz

Hi, I've got an odd problem, and I hope someone can help.

I've recently purchased the U.S. version of Tales of Symphonia, and have tried to get it running on my PAL wii.
My Wii is running 4.3E, and has Region Free Everything enabled to bypass Nintendo's illegal region locking (illegal in Australia, at least - not that it has stopped them from implementing it here).
The game is detected in the Disc Channel, boots just fine, and works... except, the graphics are oddly garbled. My console is running at 480p/60hz - but, despite being an NTSC game, Tales of Symphonia forces itself to 50hz, displays with black borders, and has a second image of the screen interposed over the first giving a weird double-vision thing.

I've tried different cables, different video settings, no change. This is driving me nuts! My TV has complete support for all current video formats, so that can't possibly be an issue.

Besides which, it works perfectly at 60hz through loaders in The Homebrew Channel, but I don't want to boot it that way! I bought a retail disc, I should be able to boot it through the disc channel.

I don't have any other NTSC region disc to test, and any help would be appreciated.

Thanks!