I have the same problem. I have a large file (~2.5 MB) that has several
different types of formatting and some cells that are still in default
formatting as "general." Recently, the cells formatted as "general" changed
to a "date" format. I checked empty cells and they have the default "date"
format, too. When I first noticed this issue, I had an older version
restored from a backup. Yesterday, it happened again and I asked for another
old version to be restored from backup. The new backup version has default
set to "date" AND the older version that I had restored a few weeks ago also
now has the default set to date.

I, too, want to know how to fix this file because recreating it or finding
all the cells formatted to default will be extremely time consuming.
I am working in Excel 2007 and the file has been converted to 2007 (although
it was probably originally created in a version of excel even before
95-2003).

Lea from CA-- I'm sorry not to be able to answer your issue, but you are not
alone... :)

"Lea from CA" wrote:

Up until a few weeks ago all was well with Excel07. Then it started to
change the default number format to a date format. When I import a file to
excel or do a copy paste, excel automatically formats numbers as dates.
Suggestion was to create a template and save in xlstart but then everything
will be formated as general. why did excel stop automatically detecting
number formats? how can I change the default settings?