Button that executes a Macro Disappear

I have an estimating spreadsheet with mulitple macros.  Along side the bid item I have a button that executes a macro that takes you to the location in the spreadsheet where the cost is determined.  At these locations I also have a button at the calculation  that will take you back to the bid item.  We have been using this spreadsheet for over 5 years (Excel 2003).  I have upgraded to Exel 2013 and occationally (twice so far) for no apparent reason when I click on the button it disappears.  So I try another and the same thing happens.  I save it and when I open it all of the buttons are gone.  Actually I have determined they have been moved, condensed, and srunk to a 10th of their original size. What is going on!!!!