ZEN REPORTS and EXCEL

I have a ZEN report set up to generate a file for loading to into excel (see attached). Even though I have DEFAULTMODE set to "excel" the resulting output file that I get on one CACHE instance is .xml while on another it is .xls. This is even though I run the report from the two instances on the same PC. Can anyone suggest what I am doing wrong? The Cache version is "Cache for UNIX (IBM AIX for System Power System-64) 2013.1.6 (Build 950_1) Fri Jun 6 2014 17:43:51 EDT"