Phew, I'm very glad someone reported this caching bug. Thanks!
I deployed a fix for this soon after my last email and confirmed that
newly-created events show up.
The underlying problem is that Rails changed the behavior of the
Observer's "observe" call in incompatible ways. As of Rails 3.0.14, it
must be called once for all models, with each call replacing the
previous values. In the earlier version that I tested my changes
against supported calling it multiple times to add values and I saw
documentation claiming that this was the better way to use it. Lame.
-igal