Probably a fudge factor adjustment to the balance sheet to make it work was corrected. Yes, this came from the K-1 preparer. It affects the basis of the shareholder and may or may not may any difference in the tax on return,  so you may not need to file an amendment. 

This is the usual of many small business. They are so busy takin' care of business, that they don't take care of the business. (Bookkeeping is not their favorite thing.)