I found that the inconsistent behavior we were expariancing with getTablePrivileges, has been logged as a bug and listed on : http://jdbc.postgresql.org/todo.html
[bugs] ACLs have changed format since the parsing code was written. The code only supports 7.3 style ACLs. DatabaseMetaData methods like getTablePrivileges do not work correctly against later servers
I was wondering if there is a timeframe by which this issue would be resolved.