Hi,
Either you go too hot, or you have been very unlucky with the wire. I had such wire a long time ago and I binned the lot and bought some new stuff - life's too short for bad wire.
Alas, if you wanna keep the annoyance factor up in what should be relaxation, you could use a bit of hot glue to keep things from shorting as an emergency solution (or RTV silicone, if it has to see temperatures below freezing).