I looked into this a bit more. It seems that the principle that a first sale exhausts the copyright is strong in the US, but not as formalised in the UK. I don't think there is any direct case law or statute on the point in the UK.
But other forms of intellectual property (patents and trade marks) do have that principle - ie once the rigtht holder releases the goods into the market, they have no control over what happens to them after that (eg resale), UNLESS they explicitly mentioned that resale is forbidden, to everyone down the chain (but even this condition is against the current general tide, which is tending to limit the rights of the originator).
The principle of exhaustion of rights should raelly apply to all fabrics, regardless of how distinctive it is, as far as copyright concerns. I guess the reason why Disney is concerned with the resale is because it might look like Disney-licensed goods. In which case it becomes an issue of passing off, or maybe infringement of registered trademark, which is a very different kind of protection compared to copyright.
So, unless the sale of the fabric was explicitly conditional on no resale, I think you are in the clear. Of course the safest thing is to ask the shop and have it in writing from them, if that's at all practical.
Hope that helps. I am, by the way, a lawyer specialising in patents....