Ok seems it was related to daylight saving somehow.
If I physically typed 6:00:00 AM after the date it remained at 4th October.
I found another report (SQL Server based) that showed the time component and if I used 4/10/2015 12:00:00 AM it got changed to 3/10/2015 11:00:00 PM whereas 4/10/2015 6:00:00 AM got left as 4/10/2015 6:00:00 AM.
Weird stuff but, work aroundable.