Behavior of file readers when file doesn't exist

I've got a SDFReader node with a problem. I validate that the file exists in both the configure and in the validateSettings methods, throwing InvalidSettingsExceptions if things aren't correct. This seems to do "the right things" when I drop the node into a workflow and configure it, including requiring me to enter a valid filename in the configure dialog before it will close the dialog (unless I cancel).

The problem appears when I configure the node, save the workflow, delete the file, and reload the workflow. I get a warning about the file not existing, but the node's state remains at "configure". Is there a way to force the state change back to unconfigured?