ActiveWorkbook.save not working with Excel 2016

[ExcelWombat]

Since upgrading to Excel 2016 my spreadsheet now saves files to a new filename in the same folder but with an unusual filename in the format "DC3E7000" or similar with no file extension. When I change the file name to have an XLSM extension it opens and displays the saved data. The original file remains unchanged. The code I use to save the file is -

Private Sub Workbook_BeforeClose(Cancel As Boolean)
ActiveWorkbook.Save
End Sub

I have tried ThisWorkbook.save with the same result. I would stress, this works perfectly with Excel 2007, 2010 and 2013 and the changes are saved to the original file.

Any help here would be greatly appreciated.
John.

 

[ExcelWombat]

Further to this problem I have just discovered that it may not be a VBA problem. I just made changes to another spreadsheet and used "Save" on the "File" menu and it created a new file called "B855A000".

I have no idea what is going on here.

I'm not even sure how to post this as a problem.