Copying to Clipboard when in Protected Mode

I'm using Excel to load incoming files not created by me, then exporting large ranges via the clipboard to another application - usually without making any edits.  I've just upgraded to Excel 2016 so I can deal in future with even larger files - ranges with more than 65536 rows.  To test the process with Excel 2016 I tried a few old files, i.e. these were in xls format.  They read fine into Excel 2016, but copying a range of any size to the clipboard makes Excel hang, usually at the point when I try and minimize Excel to load the other application.

After a lot of experimentation I've discovered the workaround - click on the "Enable Editing" button at the top of the screen, which switches off 'Protected Mode' (though still in 'Compatibility Mode').  The text on the yellow information bar said "Unless you need to edit, it's safer to stay in Protected Mode".  So I did stay in Protected Mode as I didn't need to edit.  And this apparently causes the problem - though it's not clear why.  I thought I had loads of memory (4GB), running on Windows 7 Professional 32-bit.  I never got a message saying 'short of memory', just a freeze with no clue as to what was happening.

I'm posting this information in case it's of use to anyone else.