Incidentally I know EXACTLY what caused this because I had to go poking around for something else.
And I have to say, it's sheer fucking incompetence. I left them a comment on Github as to what's wrong and why it's wrong. I don't see how he even tested it.
For those playing along at home, Lab added a feature whereby users can set the registration mode (no registration, immediate registration, member approval etc.) during registration. Except the genius managed to put the query into the code BEFORE THE SETTINGS TABLE IS EVEN MADE.
Now, he's already convinced I'm trolling him (cf. the comments on 2.1's repo from HappyTroglodyte which he thinks is me, when it's not) so I left the commentary here and left merely a factual report plus a suggestion *there*.
Now I've broken the installer in the past, but I wouldn't commit something I clearly couldn't have tested properly (or if I do, I leave a note to that effect)