I have figured out that this only happens when you're loading a texture that doesn't have alpha info (such as a 24-bit png), but you have the 2 flag on. For some reason the alpha pixels seem to default to some middle value instead of pure white, and since the image doesn't provide any alpha info to override it, you get a partially transparent image.
This seems like a bug to me, where the default alpha channel value should be pure white instead of whatever it is now.
This seems like a bug to me, where the default alpha channel value should be pure white instead of whatever it is now.