I have a similar issue but this involves dates - transaction validation rule. Any thouhgts on this issue?
see link SAP Agentry {Eclipse Editor} - Transaction Validation Rules
Ashish mentioned: "You have a setting in the object property to set blank if the value is not set. I think It will help you to validate the user has entered some value or not." I agree however in my case field B is only linked to Transaction property and not Object property. Field A is linked to object property and the same field exists in the backend app. When field B is updated with new date and Xmit is performed the new value of field B updates field A in backend app through java code. I hope I've painted for you the best picture of the scenario...