BTW, the error in Windows that originally sent me down this rabbit hole is one that I can't reproduce. But I note that it occurred following my use of the multi-maker to update a whole raft of skin demo albums. I got another error during that run, in which fairly simple diacriticals in some slide captions, like Marmorè, showed up in the album as garbage characters. Re-making the album in the foreground cured it. And running the multi-maker again, with just that one project, didn't produce the same error again. I also got one "nonsense" error message, involving a missing variable definition in a skin that doesn't use that variable name anywhere, for anything.
In short, there's some evidence that somewhere, there's a buffer overflow, and running a bunch of simultaneous album builds is enough to trigger it. Just something to keep in mind.
And I'm not doing anything illegal, immoral, or fattening, like using multiple project files in a single project directory.