After a few weeks of use, the Zar polyurethane is starting to peel right off the nylon skin near the stern. Has anyone had a similar problem, or suggestions as to what I did wrong, or ideas on how to salvage the situation before it gets worse? So far its only one area, about a foot by six inches, but fear it will continue happening. I just got off the phone with the nylon manufacturer, who assured me the nylon was not coated in any way and they had not received any other reports of this happening.

The details:
Zar exterior oil-based polyurethane, gloss
Kavon 8 ounce nylon
Skin dyed with acid dye
Coated with 5 thin coats of Zar exterior oil-based polyurethane, gloss
I sanded after the third coat only

I did not rinse off the boat or wipe it with mineral spirits after the dye set-should I have done so?
I kept the first coat of Zar thin and did not press it into the fabric-would that have helped?

Thanks,
Jeff