dplyr doesn't preserve data frame classes

dplyrclass.R

## make a data frame with a new class

d=data.frame(x=1:10,y=rnorm(10))
class(d)=c("foo","data.frame")

class(d)
## [1] "foo"        "data.frame"

## ordinary subsetting and subset preserve us:
##
class(d[1:5,])
## [1] "foo"        "data.frame"
class(subset(d,x<5))
## [1] "foo"        "data.frame"

## dplyr filter doesn't:
require(dplyr)
class(d %.% filter(x<5))
## [1] "data.frame"