melt behaviour with indexed but non-unique dataframe column names

[DavoOZ]

Hadley et al.,
As a regular user of the excellent reshape2 package, the following behavior of melt() surprised me:

Simple dataframe:
in.df <- data.frame(AA=c(1,2,3), BB=c(10,11,12), CC=c(13,14,15))

melt() works as expected
melt(in.df, id.vars=c(1))

But my dataframe has duplicated (non-unique) column names
names(in.df) <- c("AA","BB","BB")

This doesn't do what I want
melt(in.df, id.vars=c("AA"))

So, I use indexing (rather than renaming the columns).
melt(in.df, id.vars=c(1), measure.vars=c(2,3))

The dimensions are as expected, contents are not.
Should melt_check() abort if measure.vars names are not unique?
if(length(measure.vars) != length(unique(measure.vars))) { stop("names of measure variables are not unique: ", vars, call. = FALSE) }

Thanks again for creating an essential tool.

[DavoOZ]

I just noticed that this is also the subject of pull request #66.