The "Integer" field type only supports 10 characters for its max length. UPC Codes are an industry standard and frequently exceed this length and must be validated as an integer (not string or decimal).
When you enter a valid UPC number into a field designated as integer it will provide an "expected integer" error and reject the input.
Converting the field to "string" type is a temporary work around but causes us to lose the validation of requiring an integer.
Please file a formal request to extend the max character length on "Integer" type fields from 10 to at least 15.