I've been experiencing the same issue in Excel 2010 and could not find any other reports of this problem anywhere. If I'm not editing a cell and just navigating in Excel, Ctrl + Shift + Down will correctly select a range of cells. However if I'm trying to select a range of cells as an argument to a function in a formula, pressing Ctrl + Shift + Down saves the formula where it is (if possible) and then selects cells below the active cell.
After some experimentation I think it's related to formatting. For me, the error starts to occur immediately after opening a web page file saved with an .xls extension. It is an "Excel" report generated out of Oracle BI Publisher with various formatting. After the report is opened, the error will occur in all open workbooks and will continue until Excel is restarted, even if the offending report is closed.
If I copy the report range to a new workbook, save that workbook as an actual Excel file (.xlsx) then close Excel; then opening that new workbook will also trigger the issue and it remains until Excel is closed again.
If I instead open the report, Clear Formats and then save the workbook as an actual Excel file; then the issue remains while Excel is still open, but after closing Excel and reopening the new workbook the issue is gone.
So, it seems some issue with formatting can trigger this issue that will persist until Excel is closed. If this issue is occurring for someone else, I suggest the following actions if possible:
1. Close Excel entirely
2. Open one workbook at a time, testing creating a formula each time, to determine which workbook is triggering the issue
3. Copy required data and formulas from the offending workbook; or remove all formatting from the offending workbook and resave
4. Close Excel again and avoid opening the offending workbook
If this isn't sufficient, some further investigation may uncover exactly what formatting is causing the issue.