Some guys already asked it in the forum and I got the same issue.
It would be better for Terminate Workflow, if it is not mandatory to get an Pop up error message after termination. It woulb be better to have the option (maybe of creating own Messages) because the user have to click on the Pop up to close it. That is unpractical in some cases.
I think it must be a small issue to customize that but very useful indeed.