Any Adobe Acrobat gurus out there?

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But seriously, folks, can any of you fine readers explain why a calculated field on an Acrobat form would suddenly start concatening the values in its component fields instead of adding them together? On the day the project is being moved to production? And why replacing the calculation Javascript in that field with the Javascript in another field that does something similar, then changing the field values in the code as required, would solve the problem?