RPostgreSQL: datetime convert as date

Question

I'm using the RPostgreSQL package to load data from a PostgreSQL data base.

The problem is that a datetime column (POSIXct) is automatically convert into a date.

library(RPostgreSQL)

drv <- dbDriver("PostgreSQL")
con <- dbConnect(drv, dbname="abc",host="def ",port=1234,user="ghi",password="jkl" )

Instead of using this:

df = dbGetQuery(con, "
    SELECT customer_id, dttm_utc
    FROM  schema.table;")

I have to use that:

df = dbGetQuery(con, "
     SELECT customer_id, to_char(dttm_utc, 'MM-DD-YYYY HH24:MI:SS') as dttm_utc,
     FROM  schema.table;")

If I don't I loose the time and only recover dates.

I noticed this probem doesn't occur if I only want the first 1000 rows. It appears almost all the time when there is more than 300 000 rows.

How can I fix this ?