Hmm, yes, the behavior is exactly as you describe. It sounds as if the behavior is intended so I withdraw the bug report, but it still seems as if the button should enable when there is only one thing that could possibly be run (a single layout in a single project). So, feature request: it would be nice (in my opinion) if the button would always be enabled even when it is ambiguous which project should be run. In the ambiguous cases, it could simply pick one based on whatever algorithm seems most appropriate. Of course, I place much less importance on feature requests than bug reports.
Thanks for the response!