From #gnome-shell:

  <kkris> davidz:  don't know if this bug is known: i have an event tomorrow
 (1.2.2011) and it shows up when i select the date, but not under "Tomorrow"
 in todays overview
 <davidz> kkris: yeah, I'm aware of that bug... it's because tomorrow is
 another month... let me just file a bug

The problem here is with ShellEvolutionEventSource

 http://git.gnome.org/browse/gnome-shell/tree/src/shell-evolution-event-source.c

insofar that we only return events from a single month. We do this because otherwise we'd get into a loop where CalendarClient would keep emitting the changed signals.

This probably involves rewriting (parts of) CalenderClient but we might need to do that anyway because of bug 641048.