I have Excel 2007 and Windows XP.

When I use the yearfrac formula, such as =yearfrac(a5,b5) where a5 and b5
have dates in them, I get a decimal which is the correct answer, the
proportion of a year between the dates, and it is the General number format.
But when I multiply it times 12 to get the months, such as
=12*yearfrac(a5,b5) or =yearfrac(a5,b5)*12, either way, the answer comes up
in a customized date format that I then have to manually change the format
back to General in the Format Cells, Number menu.

Why does it change formats when I change the formula when the answer is
clearly a general number and not a date? How can I stop it from doing that?

Is this an Excel 2007 error?

Thanks.