The showstopper bug turned out to be a configuration issue. In early builds of 3.9, we had turned spell checking off. It should now work in the XML editor, so it got turned on again. That's when I started having bizarre crashes. I didn't put the two together until Michael gave me a hand with it this morning - I had never copied the various pieces of the spell check system to my 7.3 development directory, and that was the source of the problem. I bundle all of that with the builds, so it wouldn't have actually affected the runtime - but I never got that far.

So, the upshot is - candidate build time...