Excel to prompt me to check in sharepoint 2010

Hi All,

Here's my scenario:

I have a SharePoint2010 site with an excel spreadsheet.

user accesses the site, goes to the document library then opens the document in excel 2010 and modifies it.

The user then uses the x to close the document.

Excel then asks if you want to save it. So far so good.

After saving the document, excel just closes and the document and is check out to the user in SharePoint site but I need it should prompted to check in the document. (it does my dev env)

Does anyone have any idea why the two behaviors and how to modify what
behavior is rendered. Ideally I would like Excel to prompt me to check
in the document.

Thanks,
Siv.