I don't see how this would be happening

, and I have the same mod on and it is still working. I modified the .tiffs using Graphic Converter, and also did the mask version so it looks right when you click on it - I even put comments about that in the hint you linked

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What you're seeing means that it is actually modifying the files in the System folder on login, which is rather weird. The only thing I could suggest with rather limited knowledge would be a permissions repair....