WizardStep Not Closing After Validator DENIED

Version: Windchill 12.1

Use Case: Open a Windchill folder and click 【Export List to CSV】.
The exportTable.jsp wizard opens with a wizardStep 
Add a custom validator before the standard export processing:

return UIValidationResult.newInstance(var1, UIValidationStatus.DENIED, UIValidationFeedbackMsg.newInstance( "Error message", FeedbackType.ERROR)); 

The validation message displays correctly in the wizardStep popup.
Click OK on the message dialog.

Expected Result: After acknowledging the validation message, the wizardStep popup should close safely without JavaScript errors.

Description:

When adding a custom validator to Windchill’s standard “Export List to CSV” action,
the validation message displays correctly in the wizardStep popup.
However, after clicking OK in the message dialog,
the wizard does not close properly. The browser console logs the following JavaScript error

windchill-all.js:1556 Uncaught TypeError: top.finishServerSideExport is not a function
 at PTC.exportTable.exportTableSuccessListener (windchill-all.js:1556:281)
 at handleSubmitResult (windchill-all.js:3759:62)
 at handleSubmitResult (windchill-all.js:2317:91)
 at ext-and-extensions.js:1845:156