[Exim] Possible bug in ${sg}

I've been trying to make sure no unescaped ';' finds its way into one of
my configuration variables. I tried to use the ${sg} operator to run
this regular expression on the string: s/\\*;/\\;/g

This works as I'd like it to with regular perl:

$ echo 'foo;bar\;baz\\;zot\\\;biff\\\\;bing' | perl -pe 's/\\*;/\\;/g'
foo\;bar\;baz\;zot\;biff\;bing

..but not with exim (tested with both 3.25 and 4.11):

$ exim -be '${sg{foo;bar\;baz\\;zot\\\;biff\\\\;bing}{\\*;}{\\;}}'
foo;bar;baz\;zot\;biff\\;bing

Am I doing something blantantly erroneous here, is there some
incompability with perl's regular expression that isn't mentioned in
the Exim Specification, or is it simply a bug?

--
Tore Anderson