complete() does not preserve grouping

[davechilders]

Consider this grouped_df:

d <- data_frame(
  g = rep(LETTERS[1:2], each = 3),
  x = c("a", "c", "a", "b", "c", "d") ,
  y = c(1, 2, 1, 2, 1, 2)
) %>% group_by(g) %>% print

Source: local data frame [6 x 3]
Groups: g [2]

      g     x     y
  (chr) (chr) (dbl)
1     A     a     1
2     A     c     2
3     A     a     1
4     B     b     2
5     B     c     1
6     B     d     2

complete() respects the grouping when creating new rows, but the result is no longer a grouped data-frame. Shouldn't complete() preserving the grouping?

d %>% complete(x, y)

Source: local data frame [11 x 3]

       g     x     y
   (chr) (chr) (dbl)
1      A     a     1
2      A     a     1
3      A     a     2
4      A     c     1
5      A     c     2
6      B     b     1
7      B     b     2
8      B     c     1
9      B     c     2
10     B     d     1
11     B     d     2

d %>% complete(x, y) %>% is.grouped_df()
[1] FALSE

[hadley]

For future reference, please don't provide session info unless requested - it just clutters up the issue.