[Exim] rewriting ".." -> "/" problem

I want to rewrite x..y@??? to x/y@??? with a rule
like..

*..*@REAL_DOMAIN    $1/$2@REAL_DOMAIN    Tbct

..but running through exim -d -bv gives me this:

address match: subject=a..b@??? pattern=*..*@dcs.qmul.ac.uk
a..b@??? in "*..*@dcs.qmul.ac.uk"? no (end of list)

How stupid am I being here? (Exim 4.04.)