isdst

Can someone, please, explain the difference is results below (notice
the isdst value)

unlist(as.POSIXlt('2005-7-1'))

sec   min  hour  mday   mon  year  wday  yday isdst
    0     0     0     1     6   105     5   181     1

unlist(as.POSIXlt(as.Date('2005-7-1')))

sec   min  hour  mday   mon  year  wday  yday isdst
    0     0     0     1     6   105     5   181     0