Unfortunately some further experimentation shows that my "fix" above doesn't always work. It also mysteriously sometimes seems to lose the fabric zone (even though it retains the material definitions) and when I was trying to work on something yesterday my saving a new one as an asset somehow overwrote a previous save in addition to making a new one. I'm pretty new to all of this so I'm undoubtedly doing something wrong so I guess I'll just keep on experimenting until at least I can get consistent, predictable behaviour. Some feedback from the vendor would definitely be nice, though.