If I set up an event as "all day", it IS visible on a monthly view on the web Google Calendar, but it IS NOT visible on the monthly view on the phone. This seems to be true of holidays, as well, which I guess are "all day" by default. The problem is only for monthly views, weekly and daily show the event on the phone. And sync is working just fine, both directions. All my calendars are set up as "synced, visible".