One more piece of information that may be useful: Excel 2003 (filed
saved as .xls) and 2007 (as .xlsm) do not actually produce the same
result as the code call ends. In 2007, I receive #N/A errors, whereas
2003 produces the single-column-sum result described in my original
post. A manual calculation call fixes the wks in both versions
however.

I have also now tried deleting and re-adding range names at runtime.
Still no luck.