Pintree, your attachment isn't a template. Templates are .xltx (or .xltm if macros are involved)
On my computer your file works fine, unmerging a cell doesn't bring up any problems.

As I earlier described, if you have a look at "options" you'll find the gridlines are set to "automatic". But above the CheckBox for showing gridlines is unchecked, results that gridlines aren't shown in the sheet. The visible borders are borderlines.