hmm interesting as this seems to work fine in 5.1.4, moreover I tested the 5.0.x versions and the first one that does work as expected is 5.0.11. It produces following output:

2017-03-07 13:46:23 INFO  CustomRunner:123 - Test: hhh11552Test
Hibernate: 
    select
        nextval ('TASK_ID_SEQ')
Hibernate: 
    insert 
    into
        TASK
        (NAME, PRIORITY, OPTLOCK, ID) 
    values
        (?, ?, ?, ?)

so talking that into consideration looks like the problem has been already fixed.