In Google Calendar Week View you can click once in the blue-shaded 'All Day Event' area to create a new all-day event, the popup shows the end date as being a day before the start date. This, if unnoticed, results in an event that will not display in the calendar. Original Safari/WebKit and Mozilla family browsers do not exhibit this problem with the same page. See attachment for evidence.
Created attachment 13381 [details] Screen shot of invalid all-day event dates Screenshot of a popup in Google Calendar showing that a single click in 520+ creates an invalid date range (start > end). Does not occur in Safari or other browsers.
Confirmed as a regression with r25261.
<rdar://problem/5446502>
Rolling out <http://trac.webkit.org/projects/webkit/changeset/19567> fixes the bug.
Spoofing as Firefox fixes the problem. They probably have Safari specific code path that relies on/works around the old behavior.
I can no longer reproduce this, presumably, fixed on Google side.