Vertica different calculations than in PostgreSQL

I have one query:

SELECT CAST(((stats.ts_spawn - 1427835600) / 86400) * 86400 + 
1427835600 AS INTEGER) AS anon_1 FROM stats WHERE stats.ts_spawn > 
1427835600 AND stats.ts_spawn < 1428440399 GROUP BY anon_1 order by anon_1;

I'm expecting to get start of the each day in a week.

Result in Postgresql:

1427835600
1427922000
1428008400
1428094800
1428181200
1428267600
1428354000

Vertica returns start of each hour of each day of the week:

1427839200
1427842800
1427846400
1427850000
... and so on, total 167 records(24 * 7 - 1)

I have no idea how to modify this query.

Copyright Notice：Content Author:「Sleepwalker」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/32480429/vertica-different-calculations-than-in-postgresql