Adobe Acrobat XI Pro duplicating files when combing files into 1 PDF file?

When I choose "Combine files into a single PDF..." and I choose my file that has 242 excel files, it duplicates almost every single file into the single PDF file.  This results in almost 600 PDF pages instead of 242.  I have run this several times and keep getting the same results, sometimes I get 560 pages, sometimes, 600 pages, it varies every time I run the program.  This is a task that I regularly perform every month.  It just became an issue the last several months.