How do I reset an item in Oracle Forms?

I want to test the input when an item is changed and, if the input is contrary to policy, change the item back to its content. To do this I am saving the starting content in PL/SQL code for trigger pre-text-item, and attempting to restore it in code for trigger when-validate-item. This technique is not working, although the validation in when-validate-item is working. Presumably I have not really saved the starting value; how can I do this? What is the appropriate trigger? Or am I barking up the wrong gum-tree?