[ESS] R-mode: forward-sexp: Scan error: "Unbalanced parentheses"

[Aleksandar Blagotić]

Let's presuppose that I have a function like this:

fn <- function(x, ...){
  re <- "^#{1,6} [[:print:]]+$"
  grepl(re, x, ...)
}

As soon as I put my cursor at the end of the line with regexp, and
press RET, I get this error:

forward-sexp: Scan error: "Unbalanced parentheses"

I cannot indent the line with regex, and error comes up, though I've
provided a valid R regular expression. Sometimes it hogs Emacs and I
need to kill -s 9 it. =/
Any ideas how to mend this?
(I'm using  Emacs 23.3.1 with ESS grabbed from SVN repos)

Cheers!

aL3xa