So the answer to my question is: "yes, it's user error"!
Ok obviously this was stupid of me. I never saw the text box. It was incredibly faint on my screen, I only read "remove partition 1" and I assumed that as the button was not disabled it was ready to do its thing!
Making the button disabled and highlighting the text box if the button is clicked would make this more idiot proof.
Thanks for pointing out my stupidity!
I now have an issue with the whole crashing and needing to be power cycled when I start a preclear with no pre check. I suspect I might have done hardware issues...