Unless we know exactly in what version of Photoshop the file had originally been saved, we're shooting in the dark.
Working in CS6 ...
As I mentioned CS6
First of all, "CS6" is not an exact version of Photoshop. For instance, if on a Mac, you should be on Photoshop CS6 13.0.6. I forget what the latest update to the Windows version was.
…Even the first time I opened the file (got it from someone else)…
I'm referring to the Photoshop version that "someone else" used, not what you're working on.
Just a clarification in general:
BOILERPLATE TEXT extracted from the FAQ:
Do not be abusive or aggressive in your tone
An aggressive, demanding, accusatory or abusive sounding post will often evoke an aggressive or abusive and unhelpful reply.
Remember, you are not addressing Adobe here in the user forums. You are requesting help from volunteers users just like you who give their time free of charge. No one has any obligation to answer your questions.
I'm out of this discussion.
Had the vector smart object been places in the psd file by some other person on another computer?
If you use Export Contents on the original SO and the edited SO are the two files of roughly similar size?
Wasn't trying to be rude. Just read your post too quickly thinking you were asking me what version I had and was responding in between work activities. Anyway, same version as me CS6 13.06
No longer have the original file, but test the smart object was placed into the file by someone else. I opened it and made the spelling correction in Illustrator and closed the vector object. The all I tried to do was save the file and it jumped up by over 400MB pushing it over 2GB.
I suspect the issue may be caused by Illustrator, not Photoshop, but if you have destroyed the original file it may be impossible to verify.
What format is the SO anyway (ai, eps, pdf)?