allow.duplicates not working?

[kaneplusplus]

From an email to bigmemoryauthors:

I've been trying to use the "bigmemory" R package but I'm having some issues when trying to remove all duplicated rows (across all columns) from a big.matrix. According to the manual I should be able to use mpermute with "allow.duplicates = FALSE", but don't think it is working. For example:

m = matrix(as.double(as.matrix(iris)), nrow=nrow(iris))
x=m[,c(1,2)]
mpermute(x, cols=c(1:ncol(x)), allow.duplicates=FALSE)

I still get duplicated lines (e.g. 134, 135 and 136).
Is it a bug? Or am I doing something wrong?