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IrrEdit uses DirectX, I'm guessing you use OpenGL and have an ATI video card, and the corrupted textures are not powers of two in each dimension. Plus you updated your video drivers between Irrlicht 1.3 and 1.5, the new ATI drivers have a bug with generating mipmaps for non-power of two textures.
I don't have an ATI test machine so I can only go on what other people have said, but I think this problem alternates between broken and fixed between driver versions.
We could do what CrystalSpace do and disable certain features for buggy driver versions, it's possible now you added setFeatureAvailable anyway.
I'm not sure though, we'd probably end up maintaining an ever-growing list of bugs from old driver versions that nobody uses anymore.