有谁能解释一下这里发生了什么?
> as.POSIXct(paste("20140329", "02:00:00"), format="%Y%m%d %H:%M:%S")
[1] "2014-03-29 02:00:00 CET"
> as.POSIXct(paste("20140330", "01:59:59"), format="%Y%m%d %H:%M:%S")
[1] "2014-03-30 01:59:59 CET"
> as.POSIXct(paste("20140330", "02:00:00"), format="%Y%m%d %H:%M:%S")
[1] NA