Try changing the Windows system locale. Whether this will have any effect here will depend on how the Office OCR works internally. It won't have any effect on your English text, but alters how unicode text is perceived. You will have to restart the PC for it to take effect so ensure that your work is saved first.
Control Panel > Region > Change Location > Administrative Tab > Change System Locale - Greek
Don't set the 'Beta' option as that doesn't work correctly ... yet.