Hey Larry,
I've used Tenara for years, and have never had any particular problem... About a year ago, I switched to the heavier M1000H, and love it. It is a much heavier/stronger thread, and did take a bit of getting used to. It doesn't like being twisted by being pulled off the cone in a conventional manner, the solution is to mount your cone like a roll of toilet paper, instead. Once I did that, I eliminated any issues with twisting and bunching up at the needle, and have found it very nice to work with, especially when passed thru one of those little lubricating jars before entering the machine...
Good tips from Sailrite on using Tenara here:
I made a new sailcover this winter, and with this heavier Tenara it definitely has the feel of something considerably more robust than my previous one...
best regards,
Jon