[R-Forge #5647] Mysterious crash with := and NAs while grouping

[arunsrinivasan]

Submitted by: Arun ; Assigned to: Arun ; R-Forge link

The title may not be appropriate (as I've not looked into the issue yet, just that it crashes the session or gives a warning occasionally):

Code on behalf of Zack:

library(data.table)
dt<-data.table(strip="Nov08",date=c("2006-08-01","2006-08-02","2006-08-03","2006-08-04","2006-08-07",
                                    "2006-08-08","2006-08-09","2006-08-10","2006-08-11","2006-08-14"))
dt[,forward_date:=c(rep(NA,5),date),by='strip']

It crashes or gives error: Link