This question is best posed as feedback - third icon from top right in the APEX 5 builder, or further info at the app address
I would check your browser console log, and provide details of browser - have you tried a different one?
Also compare buttons & relevant components to the sample application. Does the sample application work properly for you?
After doing some reading, it turned out to be the fellow behind the keyboard. There is apparently a close dialog process which needs to be used and this will do what I was looking for. For anyone else who is curious see http://blog.iadvise.eu/2014/02/10/apex-5-0-modal-dialogs-have-never-been-so-easy/#comment-29067http://blog.iadvise.eu/2014/02/10/apex-5-0-modal-dialogs-have-never-been-so-easy/#comment-29067.