I get the same result if I try to create two pages with the same root entity, except I get a clean dialog box indicating an exception in System.IO.File.Move(): "Cannot create a file when that file already exists". Clicking OK aborts the wizard actions, but allows closing of the wizard and continuing with Visual Studio. I'm very surprised that you don't see the dialog box. In any case, I should pre-check for this condition and signal an error during wizard data entry.
If I do the same thing, but provide a unique name for the summary view, it runs OK. Please double check that the name you are specifying for the summary view does not conflict with any files in the Views folder.
It also works OK for me if I choose None for the summary view option or if I select Existing and type in the name of an existing summary view (the combo box is not yet populated with existing view names). Please try these options and let me know the results.
Late-breaking news:
Before I clicked "Post", I tried one more option and was able to reproduce your "Bonk but no dialog" result.
If files with the name you specify for the SummaryView exist in the module folder (as opposed to the Views subfolder of the module folder), then I get the behavior that you see. Please check that your module folder does not contain any leftover view files (viewname.cs, viewname.Designer.cs, viewname.resx or viewnamePresenter.cs) from failed wizard runs.