Date conversion with as.POSIXct and as.POSIXlt (PR#9196)

[...]

I'm not sure any of this is actual bugs (Brian will tell us soon
enough), but it does appear at least to be underdocumented.

(Your message crossed mine.)

I think it is not a bug and actually explicitly documented in ?as.POSIXlt.  
What may help those who have not read that documentation is to stick the 
UTC timezone on the conversion to POSIXlt.  Getting

as.POSIXlt(Sys.Date())

[1] "2006-09-01 UTC"

as.POSIXct(as.POSIXlt(Sys.Date()))

[1] "2006-09-01 UTC"

as.POSIXct(as.POSIXlt(Sys.Date()), tz="")

[1] "2006-09-01 01:00:00 GMT Daylight Time"

might be helpful to non-readers.

Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595