Compatibility issue - 2003 -> 2013

Hello. I attach a workbook. It has macros in it but the macros are not the issue.
The workbook was created in Excel 2003 and worked fine under that version.
It also works fine (so far, testing incomplete) if opened in compatibility mode in Excel 2013, ie preserving .xls format when saving.
But if I try to save it as a .xlsm file in Excel 2013 it presents a peculiarity:
Then, it dislikes two of the defined names, "Ref1" and "Ref2" (localised to sheet "stmt (0)", which evaluate to #REF! error.
Note that these names evaluate to #REF! error while in .xls format without causing any problems in Excel 2003.
Anyway, Excel 2013 insists on renaming these defined names as "_Ref1" and "_Ref2" respectively.
But what also seems particularly odd is that these are not the only two names which evaluate to #REF!. For example the name "Date2" which also is local to "stmt (0)" is almost identically defined and also evaluates to #REF!, but conversion from .xls to .xlsm leaves that defined name intact.

None of these names evaluate to #REF! once the macro to Add Rows has been run, and I would much prefer to leave "Ref1" and "Ref2" names as originally defined.

Any ideas what is going on?

Thanks