I suppose, having not tried, that warning (at runtime) is new and is shown only in B4XPages projects.
However, since I need an Activity (or more?) with a different orientation than the B4XPages of my project, I set it as "unspecified" and then I used the ScreenOrientation method (library Phone) in each Activity and this seems to work without problems, so I think I can ignore that warning .
Right, as Erel said in the B4XPages thread:
1. You are not forced to use B4XPages. All the current features behave exactly as before. 2. B4XPages is currently in beta version. The API is not final, things might change.
3. It does have some limitations. One notable limitation is that in B4A, the activity that holds all the pages should be locked to a single orientation.
4. It is supported by the latest versions of B4J, B4i and B4A.
Thanks, I know all that; I just noticed that warning and thought it's new and that it is just that, a warning, ignorable (if you use SetScreenOrientation, as I did).