I know you checked this but here is some more info that will point you in the right direction.
From the MSDN,
KB Article:XWEB: Day or Year Inconsistencies in Outlook Web Access Calendar View
Q253964
Outlook Web Access clients pull their date and time zone information from the server running IIS and OWA. In other words, the date and time zone context that you are in when you log on to Outlook Web Access is defined by the location of the server running IIS and OWA. This is what can cause amessage to appear to arrive earlier or later than it was actually sent. An exception to this rule is the two-month calendar view that is displayed in the right pane of a personal calendar. This pane is generated by a Java applet and pulls the local day and year information from the computer that the browser is running on.