Just fix your timezones in your config or server.

The best example is in this Xoops site: http://xoops.peak.ne.jp
It seems that the site is set to time zone GMT+9 (Tokyo, Seoul, Osaka…)
There is an event (orange dot) on May 11th (Event = Mother’s day)
You can see the problem this way:
Change timezone from your profile to GMT+8
Go to May 2008 in MiniCalendarEx
The event is now on Saturday 10th of May!
And if you click to the orange dot there is no event (of course because the event is on Sunday!)
This problem happens in Mini Calendar too (it is the previous day of the event witch is underlined)