[ESS] M-; makes double hash in R files

[Tamas K Papp]

Hi,

When I open an R file with ess, typing M-; on a line which has
something on it puts a ## comment mark like this:

a <- 1 ##

If I delete one of the hash marks and type M-; again, the comment is
correctly positioned, eg

a <- 1                                  #

What can I do to get the single hash mark (correctly positioned) by
simply typing M-;?  I am using Ess 5.2.6-1 in Emacs 21.4a-1 (both
debian testing).

Thanks,

Tamas