If I use the 'No view for transition' (e.g. remove the extra dialog page) option for the transition and the Validator check kicks-in a run-time exception occurs:

HTTP Status 404 - No view for result [error] exists for action
[WorkflowUIDispatcher]

type Status report
message No view for result [error] exists for action
[WorkflowUIDispatcher]
description The requested resource (No view for result [error] exists
for action [WorkflowUIDispatcher]) is not available.

It seams like Jira is confused where to display the validation result.

To reproduce: Simply create a validator and select 'No view for transition'