To many records returned

Have a select statement with a where clause using datestamp with
timezone column compared to a date

Select * from sometable where DateStampColumn > '2008-03-31'

this returns records that are equal 2008-03-31

but when the query includes casting to date
Select * from sometable where DateStampColumn::date > '2008-03-31'
The result is correct

What is causing the difference in the results

My guess is '2008-03-31' is being cast into a datestamp value of
2008-03-31 00:00:00.00-00  which would explain why one query returns
more records.