A PortalSessionActivationListener object is set as an attribute in the session. When the session is shared with other applications then ClassNotFoundException is thrown since PortalSessionActivationListener is coming from portal-impl.jar that is not available for other web application.
The final decision was to take the issue into two parts:
(1) Open an LPS bug to wrap the object into a TransientValue so that it doesn't get serialized
(2) Open another LPS bug for the need to cache the CMIS session into the HttpSession for performance of the CMIS adapter in doc lib.
This LPS is for part (2)