TIMESERIES return strange results

Hi I run the below query TIMESERIES on top of dc_process_info_by_hour table , i use it as a demo for my team , in order to present the abilitys of this function . The query is : SELECT SLICE ,TS_FIRST_VALUE(resident_size_sample_sum IGNORE NULLS,'CONST'), TS_FIRST_VALUE(resident_size_sample_sum IGNORE NULLS,'LINEAR') from dc_process_info_by_hour where time at time zone 'GMT+2' >= '2013-05-21 16:59:00' AND time at time zone 'GMT+2' <= '2013-05-21 20:00:00.0' TIMESERIES SLICE as '20 minutes' over ( order by time at time zone 'GMT+2' ) However the output i get is strange , see attach , i am expecting that the SLICE of the 2013-05-21 17:00:00.0 giving te fact that this is hourly table and when i query the data without the TIMESERIES i see data for 2013-05-21 17:00:00.020849