When STATE_SAVING_METHOD=client, Trinidad blocks delegating calls to saveSerializedView() in SeamStateManager, which makes that conversations propagation does not work. Conversation context cleanup is never triggered.
I filed a bug to Trinidad's JIRA: http://issues.apache.org/jira/browse/ADFFACES-261
But the Trinidad team thinks it's a Seam's fault and StateManager should not be used for this kind of things.
Anyway, I wanted to warn those who want to try Trinidad with Seam: don't use client side state management. Take the latest Facelets version, which is currently 1.1.11, otherwise Seam will not work with the server side state management.
I have solved this issue by changing the way Seam tracks conversation ids.