Postgres JDBC driver seems to not handle UTF-8 clobs correctly. When you retrieve the clob the characters are not correct (you get ? marks for non ascii characters).
Adding @Type(type="org.hibernate.type.StringClobType") to the clob description in hibernate solves it for me.
clob? You mean text or varchar, PostgreSQL doesn't have clob datatype. The PostgreSQL JDBC driver doesn't have problems with that, it would be useless without UTF8 support. It works fine over here.