 One relevant factor here that might influence accomodation is information structure. In (40b), the cleft structure might be said to reflect the presence of a Question Under Discussion (QUD), in the sense of Roberts (2012), concerning who solved the problem. To the extent that such a question is under discussion, the interlocutors will presumably know that this is so. And if "Who solved the problem?" is indeed the question the interlocutors are trying to answer, then they are likely to mutually accept that someone solved the problem, thus explaining projection. Crucially, this line of reasoning depends on the cleft in (40b) having a particular information structural function, and a similar argument could not be made in a case like (39a), where there is no constructional marking of information structure, and in particular no indicator that "Who solved the problem?" is the QUD.