One potential cause of Excel not duplicating a worksheet comes from long worksheet name and duplicating that worksheet multiple times.
You can replicate the issue by naming a worksheet "abcdefghijklmnopqrstuvwxyzabcde" (i.e., the max number of characters allowed by the worksheet, which is 31 for my 32-bit version of Office 2013). Then, duplicate the worksheet once, so that you get a copy of the worksheet named "abcdefghijklmnopqrstuvwxyza (2". At this point, if you duplicate the worksheet again, you will get an empty worksheet--i.e., the issue with Excel not duplicating it.
The problem is due to Excel wanting to name the copy "abcdefghijklmnopqrstuvwxyza (2" again, but a worksheet with that name already exist. So, the duplication failed.
I am not sure if this technically is a bug - perhaps just poor beta testing.