Thanks csimon, but I'm a bit confused about your request for further screenshots.
On the 2 pdfs showing the details of the views, each has the Theater View "Options" panel, with the relevant view selected, and (further down the PDF) for each view, the "Edit" dialog for the only item in the Details list, which in both cases is TitleA, and the "Set rules for file display" dialog (headed "Edit Search") for the view.
And yes they do look as if I've accidentally copied the wrong images. When I said I'd made them identical, I really meant it. the selection criteria are the same, there are no options set, etc. I can't think of any reason why they should behave differently. But equally, I recognise that I'm a mere novice compared with some of you guys.
I see what you are saying about the Play All item on the intermediate screen, and yes it's a good clue about looking for a possible bug (20 years in software development). It's probably stating the obvious but in the example shown, there is only one item. Redoing the test with a movie where I have multiple versions, the intermediate screen is definitely Coverflow.
And now it gets interesting. On the Intermediate screen, as well as Play All, you can also go More > Toggle List Style. All of the usual suspects are there, and if you select any the multi item options (like Coverflow) the behaviour remains the same. But if you select the detailed item style (i.e. what you get at the lowest level of the query, the behaviour changes, and the intermediate screen is no longer shown. The behaviour of the 2 views is then identical. Furthermore, as there is no "More" option on the detailed screen, you cannot go back to reset the List Style.
So (like you) I'm guessing that its an issue with the code that controls whether you drop through a view level if there is only one item. Maybe a flag somewhere is being set differently for a default view than for a manually added one.
In the interest of complete disclosure, although I don't think it's relevant, I'm testing in a client/server setup. It's much easier to test the different behaviours on the client side (especially when they cannot be reversed!) as restarting the client resets the views to the ones on the server. I've just checked the settings and behaviour on the server, and they are identical to what I've described above. The one thing I havn't done is toggle the list style on the intermediate screen on the server. Although this would "fix" the problem, it would also make it much much harder to replicate / test it.