Excessive memory used in Excel 2013 during range merge called through VBA

Hello,

Our organization is in the process of migrating from Office 2003 to Office 2013 and from Windows XP to Windows 7. So far the process is going smoothly, however about a week ago someone contacted me because they were having trouble with a particular Excel report they used to generate. The workbook is an Excel 2003 workbook which contains quite a bit of VBA code which pulls information from various SQL tables and then formats the information. When I began looking at the code I noticed that there were a couple of places where a range of cells was being merged.


One sample of code looks like:

Call Range(Cells(CStr(NUMBER_OF_ROWS_MORE_THAN_ROWCOUNT_TO_FAMILY_LIST + NUMBER_OF_DETAIL_ROWS), PRODUCT_CAT_FIRST_COLUMN), Cells(CStr(NUMBER_OF_ROWS_MORE_THAN_ROWCOUNT_TO_FAMILY_LIST + NUMBER_OF_DETAIL_ROWS + Cells(NUMBER_OF_DETAIL_ROWS + NUMBER_OF_ROWS_MORE_THAN_ROWCOUNT_TO_FAMILY_LIST, CATEGORY_COUNT_COLUMN)), PRODUCT_CAT_LAST_COLUMN)).Merge(True)


Now this is pretty hard to read because it includes a number of constants, but essentially the code is trying to merge about 1 column with data together with the 24 empty columns beside it, for about 600 rows.


The original developer is long since gone so I can't ask why they did what they did, or how, but I can tell you that in Excel 2003 this line runs without so much as a hiccup. On Excel 2013 memory usage for the Excel process shoots from between 90-130MB up to 1.4GB and then settles back down. I'm trying to understand why there would be such a dramatic difference in behavior between the two versions of Excel, and what I can do to fix it?

Any suggestions are welcomed.

Thanks,
Troy.