Thanks for reporting the issue. It might be a bug that has something to do with the time zones (that's tricky sometimes). I have a few questions:
1. Is the online demo (
http://www.daypilot.org/demo/Calendar/MonthView.aspx) corrent or not?
2. What's the culture that the page is using?
3. What's the time zone set on the server?
4. What's the time zone set on the client?
5. What's the number in the cell in the upper-left corner (the first one)?