John, I’ve done as suggested however now I can’t reproduce the issue!
I downgraded PHP from 7 back to 5.6 and attemped the page update again and the blank value is now saving as it should. The post array was as expected, the field was present and empty and that was saved to the database.
I would say the issue is related to PHP somehow, either a setting in php.ini, mod_security rule or perhaps Suhosin (but I don’t think Suhosin was the issue).
Thanks for your help.
