Why does Excel spreadsheet lose format changes after saved?

[txlogic]

I have Excel 2007 but have to save files in 97 Format (.xls). I have a
spread sheet that I have formatted the cells for accounting, number and
percentages formats. Everything looks great until I save the file, than when
I re-open it all the formatting changes I made are gone, but if I save the
file in .xlsx format everything works fine. Unfortunately, several of the
users who need access to my file are still using 97 Excel; so, I have to find
a way to save this file with the proper format.

 

[Hrafnkel]

I have been having the exact same issue over the last six months or so. The
problem only seems to be getting worse. I have scoured the internet looking
for solutions, but I'm unable to find any concrete reasons as to why this is
happening. It would be awesome to find a resolution to this.