Comment 5 for bug 302698

In related news, I think I've found a (the?) major cause of this problem in newly created repositories. When pushing a new branch to Launchpad that
 a) triggers the "Using default stacking branch" logic, and
 b) has a source branch in an unstackable format,
it appears that the first push will push a stacked repository, and then put an unstackable branch format on it. A subsequent push finds an unstacked branch, and thus also finds that the target repository is almost certainly missing parents for any delta records it adds. I'll send patch to the list shortly.