Excel 2007 dropdown error in excel 2010

Hello,

In excel 2007, I used Data validation list (drop down list) which retrieved data from another sheet and it works fine in excel 2007.
However, once I open with excel 2010 the same sheet(without changing anything), the drop down list contents are vary.

For example,

I retrieve data from another sheet called 'Month'

=Month!A1:A5 in excel 2007

when I open in excel 2010, this drop down list valued auto changed to
=Month!A4:A8

I would like to know how to fix that. Thanks in advance.