Jay, I hate to see your post go unanswered so I'll give my brief experience. Hopefully someone else can chime in

I only reared a couple of cultures of these guys many years ago, but I recall them spinning as you describe in a very obnoxious manner. I was actually surprised at the amount of "silk" production of these larvae; especially compared to actual silkworms (Bombyx mori). All of my waxworms behaved exactly as you are describing for your F1 generation of larvae - although I purchased mine directly from a local breeder rather than a commercial source.

I'm actually half-tempted to message a commercial breeder about this inquiry, its interesting. I've heard of this happening before so you're not the only one... perhaps something with the shipping or refrigeration process does something? No idea, just speculating...