Since you're sanding the floor to refinish it, why are you cleaning it with TSP? The 'acrylic-like' look is probably just more poly. As you're already doing, keep the paper 'new' and keep vacuming. Once you're down to the wood, only take off about 1/8" or so. That should give you enough flooring to stain and re-poly.
The TSP may be loosening up the poly and reacting w/it when it's heated under the sander too. I'd stop using the TSP.