Lazy eval, dplyr "filter" and NAs

I am having some silly problem using lazy evaluation and dplyr. I'm trying to filter some NAs and don't know why the lazyeval version doesn't work. Probably I'm missing something, but I can't find it. Is that so, or is it a bug?

Here is a minimum reproducible example:

library(dplyr)
library(lazyeval)

data(iris)
iris$t <- c(1:140, rep(NA, 10))

#This Works
temp <- filter(iris, !is.na(t))

#This doesn't
temp <- filter_(iris, interp(~(!is.na(x)), x="t"))

Both codes run without throwing out an error.