Some more data in case it helps. I installed and ran Hex Workshop 4.1 to see if the data in the headers was the same - it is not.
From the 1.63 files, which are 3,000,026 bytes long:
From the files MS Paint in Windows XP Pro saved after being altered, which are 3,000,054 bytes long:
Now this may not make sense to anyone, but it's the first 4 lines of the files as viewed in Hex Workshop. And it clearly indicates the header data as saved by the mud doesn't match what XP is saving from Paint. So there's no surprise the resulting reload from the mud would get fubared. Apparenly it's overwriting memory it shouldn't be. I being the graphic file unsavvy person I am can't offer a suggestion as to how to overcome this problem.