This is a harmless warning from Hibernate and has been suppressed from making it to the atlassian-confluence.log file, but is still present in standard out.

These warnings can be suppressed, however. To do so please open confluence/WEB-INF/classes/log4j.properties and find the following line:

# suppress warnings from the SessionImpl (like Narrowing proxy to class com.atlassian.confluence.pages.Page - this operation breaks ==)
log4j.logger.net.sf.hibernate.impl.SessionImpl=ERROR, confluencelog

Underneath that add the following line:

log4j.additivity.net.sf.hibernate.impl.SessionImpl=false

This additional line will stop these warnings from being logged to standard out, such as the catalina.out file.