The other thing you may be running into is holes from the slicing machine used to cut the fabric into thinner strips from the original 60" bolt. I do this slicing too, but I don't have some fancy machine that does it at 20 yds./min. I rember seeing something like this at the UK factory and thought it was a good idea at the time but everything I tried to duplicate the process left the same lines of tiny holes where the tension wheels are.
Don't know this is your problem for a fact, but seems likely from the process used at UK.