Consider the following scenario in Microsoft Office Excel 2010:
You have a worksheet with two or more rows frozen at the top of your worksheet.
You have two or more cells lower than row 1 inside the frozen area merged horizontally.
One of the columns that contain one of the merged cells is the frozen area is aligned next to the row headings in the leftmost visible column (rightmost column for right-to-left languages such as Hebrew and Arabic).
In this scenario, if you click the row heading of a row that contains the merged cells above the frozen line, multiple rows will be selected.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
We recommend you follow one of these methods to work around this problem:
Method 1: Click and hold the mouse button when you click the row heading.
When you select the row heading, click and hold the mouse button on the row heading instead of using a single click. At first, multiple rows will be selected, but shortly afterward, the selection will revert to the single row you selected.
Method 2: Scroll the page
Scroll the page left or right so that the rows containing the merged cells in the frozen area are not next to the row headings.