dmen68

Something somewhat similar happend to me.  Here is how it went down:
I got married and had been on va pension.  I got pension because the wait on compensation was forever.  
Well, after I married a nurse I was no longer eligible for pension because my household income was too high.  I knew this, and reported it the month I got married.  
So, in typical VA style, they kept sending me pension (overpaying me) for about 2 years.  They FINALLY took me off pension, and sent me a letter that I owed them $6000.  
I filed a "waiver" on the repayment, arguing that:
1.  I told them about it, and its not my fault VA takes 2 years to process this.  
2.  Taking the money back would be a hardship, as I do not have access to my wife's money.  Its hers, not mine.  
      In about a few months, they approved my waiver, and I did not have to pay the money back.  However, when I eventually got my full 100 percent plus SMC S, retro, they took back the money in retro, so there was no free money.  
My advice is to document the overpayment AND probably tuck the extra away and expect to have to return it.  
      If you had lied to VA, you may be in trouble.  I did not.  Again, VA inefficiency in processing claims is hardly our fault.  
      Other Vets have reported they got temporary (SMC) from something similar, and VA NEVER stopped it, even tho they reported it.  Our highly inefficient VA actually works to our benefit sometimes, tho it usually goes the other way.  
     My advice is to heed the above, and, if applicable, apply for an increase or additional disabilities.  If you are still working you are not likely eligible for TDIU, but, if conditions have worsened since your c and p that got you your rating, you still may be eligible for an increase.  

So, do I have it right that you think you are being overpaid?  Have you looked in the "letters" section of ebenefits?  (Assuming you are missing some VARO decision(s) which awarded benefits you may not have been aware of.  
If you go to your VSO, you should be able to get him to look at your VBMS file, and it should show the disabilities you are rated for.  Perhaps you have been increased, such as tdiu, and you were unaware.  
This sounds like a temporary 100 percent rating while you are recovering from surgery.  A temp 100 percent, plus your 80 percent qualifies you for SMC S 1, yes.  Generally that is for a year to recover from surgury.