1) This has not personally happened to me and I will keep using the armory with my gems. If I lose a gem... I'll have to level it back up. Sucks, but I don't want to give up on the flexibility and most desired feature that the armory provides.
2) To people who doubt this or even call it a hoax: read the bug reports provoss linked. As I said, it hasn't happened to me - but there's actually too many people who reported this bug to make this a hoax. I think the title is misguided (I'll edit it to something more appropriate and less misleading) - but it's a nice heads-up for everyone who wants to take precautions for potential bugs. If you got a rank 120 Trapped gem through some crazy upgrade luck I'm sure you'll appreciate the extra safety warning by the community.