This is a setting that you can change in Excel.
Use Ctrl +A (Cmd + A on Mac) to highlight the whole range and then click the Unmerge cells button/link.
If you can't find the "unmerge cells" button you can go to View/Toolbars/Customize and then search for it on the "Commands" tab under the "Format" category.
This page at Microsoft.com has some tips: Merge and unmerge cells
Updated 7/13/16