OnExecutorFinishedDelegateNative and OnExecutorFinishedDelegate broadcasting an bFatal into a bSuccess parameter which is inverted. Canceling a render should be considered an error, not a success.
In MovieRenderQueue widget
Add a sequence
Add a map
Press X to close the render mid render.
(See comments for more detailed description of what needs to be changed)
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-160482 in the post.