[Rd] as.Date() , feature or bug?

[Bo Peng]

Under linux and windows,

> as.Date("6666-06-06")
[1] "6666-06-06"
> as.Date("7777-07-07")
[1] "1970-01-01"
> 

Feature? Bug? help(as.Date) does not mention this case.

Bo.