I recently needed to create several multi-day events. After entering the first day's start date, time, and end time, I clicked "Add another occurrence" and checked the "This is a multi-day event" box. After adding more occurrences, the finished multi-day event worked exactly how I wanted to: it showed up only once in the upcoming events widget with a date range, but also appeared on each date it spanned in the big calendar. The pop-up windows and event detail pages all showed the date range, too. So far, so good.
I realized I needed to make a change to the event info for ALL days, so I clicked on "Edit Group," made the edit, and clicked "Edit Event Group." From then on, the calendar no longer treated it as a multi-day event, but as a series of events. It appeared multiple times in the upcoming events widget, the pop-ups and event detail pages showed individual dates instead of the date range, etc. The only way for me to fix this was to delete all instances of the event and create a new multi-day event, taking care not to make any group edits later. Can you let me know if there is something I've been doing wrong? I would really appreciate any help... Thanks!