Dev UI Stockholm syndrome?

I always leave the UI design until towards the end of a larger project. I know if I start with the UI I'll end up finding parts of the system that don't fit the layout, rejig this, tinker with that, rework that bit again... I get too focused on making the UI right when it could be wrong again with the next functional change. I may as well switch individual pixels around.

To solve that, I usually knock up a quick development UI at the beginning, do all the functional work, then look at how the UI/UX makes the functional stuff display and work easily for a user.

That's leaves me in a position where I've been coding and testing in a development UI for months... And then get Stockholm Syndrome or something about leaving it behind for a professional finish.

Anyone else? Should I change my mind nd do the UI upfront? My concern with doing that is that I'll get Stockholm Syndrome for a relatively acceptable UI and just leave it. At least with a "I know I have to leave you UI" I know it's just me thinking the shitty UI I've been using for months is a friendly thing to use.