IL Artboard not staying at final size after saving, closing, then opening

[John226626956x1g]

I have run into a strange problem where if I modify the size of the artboard for my file, using Document Setup, save, close, then reopen the file, it reverts back to its original artboard size.
But now I just found out that if I create a new document at a different size, then open a file, it changes the artboard to that new document size. Totally crazy.

[John226626956x1g · Accepted solution]

I have found out that if I save the file with a new name, it keeps the artboard size to what it is set to. If I find another run around, I will let post it here.