timestamptz time is off by one hour

Hello,
When I use JDBC to insert a value into a timestamptz column, the value is off by one hour:
The value inserted by Java program is 2019-05-01 10:00:00
But the value in database is shown as 2019-05-01 11:00:00+00
This only happens for the dates within daylight savings range. If I insert a date like 2019-01-01 10:00:00, the database shows correct value as 2019-01-01 10:00:00+00
The Vertica database server timezone is UTC
I am running my java test program in my local time zone of EST5EDT. If I force my java program to run in GMT timezone -Duser.timezone=GMT, then the problem is gone.
Is this a bug related to Vertica JDBC driver?
As a comparison, I also tried Postgres DB with same testing program but no such issue exists.
Any help?
Thanks
Bin