Alpha value lost with scale_colour_manual

[hadley]

dat <- data.frame(x = 1:10,y = 1:10,grp = rep(letters[1:2],length.out
= 10))

ggplot(dat,aes(x = x,y = y)) +
       geom_point(aes(colour = grp)) +
       scale_colour_manual(values = c('#FF00001A','#0000FF1A'))

reported by Joran.

[hadley]

Closing because it's a duplicate.