5xx data displayes under "title notes" tab in the normal view. It might be better to display these fields in the same way as other fields. Many library members may not click on the tab to look at the notes.
I disagree that this is a bug. This may be a customization that you want to implement for your library but Koha has done it this way for a long time and I think it works well. I do notice that in the OPAC XSLT view the summary (520a) and contents (505a) appear with the other fields already. Now that Koha offers much better options for using custom XSLT this kind of change should be easier.
I'm with Owen here - this is something that should be done as a local mod.