A:
This is a guess on my part, but hopefully something you can check.....
My Rocketfish diffuser seems to have a fairly heavy light loss. It's possible that it is interfering with the preflash that the Canon TTL system uses to determine proper flash power & exposure.
IF that is the case, you can use flash compensation to reduce the power of the flash, and hopefully have no more blown out shots.
I don't own a 430, but I would imagine if flash exposure compensation is not adjustable on the 430, then it can be done from the T2i's menu system. Check your flash/camera manuals.
Hope this helps...